Handover Signaling for Beamforming Communications

ABSTRACT

A serving base station transmits a message to one or more target base station in response to a handover decision for a wireless device supporting beamforming and multiple carrier configurations. The message includes a plurality of measurement configuration parameters for the wireless device. The serving base station receives a response from at least one of the target base stations. The serving base station transmits a handover command to the wireless device subsequent to receiving the response message.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/577,203, filed Dec. 19, 2012, entitled “Beam Information Exchangebetween Base Stations,” and U.S. Provisional Application No. 61/577,206,filed Dec. 19, 2012, entitled “Beamforming Codeword Exchange betweenBase Stations,” and U.S. Provisional Application No. 61/577,208, filedDec. 19, 2012, entitled “Beamforming Signaling in a Wireless Network,”which are hereby incorporated by reference in its entirety.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

An exemplary embodiment of the present invention is described hereinwith reference to the drawings, in which:

FIG. 1 is a diagram depicting example sets of OFDM subcarriers as per anaspect of an embodiment of the present invention;

FIG. 2 is a diagram depicting an example transmission time and receptiontime for two carriers as per an aspect of an embodiment of the presentinvention;

FIG. 3 is a diagram depicting OFDM radio resources as per an aspect ofan embodiment of the present invention;

FIG. 4 is a block diagram of a base station and a wireless device as peran aspect of an embodiment of the present invention; and

FIG. 5 is a block diagram depicting a system for transmitting datatraffic over an OFDM radio system as per an aspect of an embodiment ofthe present invention;

FIG. 6 is a block diagram of a limited feedback system as per an aspectof an embodiment of the present invention;

FIG. 7 is a block diagram of a limited feedback MIMO system as per anaspect of an embodiment of the present invention;

FIG. 8 is a block diagram for beamforming information exchange as per anaspect of an embodiment of the present invention;

FIG. 9 depicts message flows between a base station and a wirelessdevice as per an aspect of an embodiment of the present invention;

FIG. 10 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention;

FIG. 11 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention;

FIG. 12 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention;

FIG. 13 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention;

FIG. 14 depicts an example flow chart for a handover process as per anaspect of an embodiment of the present invention; and

FIG. 15 depicts an example flow chart for a handover process as per anaspect of an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Example embodiments of the present invention enable beamforminginformation to be exchanged between base stations. Embodiments of thetechnology disclosed herein may be employed in the technical field ofwireless communication systems. More particularly, the embodiments ofthe technology disclosed herein may relate to enhancing the exchange ofbeamforming information between base stations in a wirelesscommunication system.

Example embodiments of the invention may be implemented using variousphysical layer modulation and transmission mechanisms. Exampletransmission mechanisms may include, but are not limited to: CDMA (codedivision multiple access), OFDM (orthogonal frequency divisionmultiplexing), TDMA (time division multiple access), Wavelettechnologies, and/or the like. Hybrid transmission mechanisms such asTDMA/CDMA, and OFDM/CDMA may also be employed. Various modulationschemes may be applied for signal transmission in the physical layer.Examples of modulation schemes include, but are not limited to: phase,amplitude, code, a combination of these, and/or the like. An exampleradio transmission method may implement QAM (quadrature amplitudemodulation) using BPSK (binary phase shift keying), QPSK (quadraturephase shift keying), 16-QAM, 64-QAM, 256-QAM, and/or the like. Physicalradio transmission may be enhanced by dynamically or semi-dynamicallychanging the modulation and coding scheme depending on transmissionrequirements and radio conditions.

FIG. 1 is a diagram depicting example sets of OFDM subcarriers as per anaspect of an embodiment of the present invention. As illustrated in thisexample, arrow(s) in the diagram may depict a subcarrier in amulticarrier OFDM system. The OFDM system may use technology such asOFDM technology, SC-OFDM (single carrier-OFDM) technology, or the like.For example, arrow 101 shows a subcarrier transmitting informationsymbols. FIG. 1 is for illustration purposes, and a typical multicarrierOFDM system may include more subcarriers in a carrier. For example, thenumber of subcarriers in a carrier may be in the range of 10 to 10,000subcarriers. FIG. 1 shows two guard bands 106 and 107 in a transmissionband. As illustrated in FIG. 1, guard band 106 is between subcarriers103 and subcarriers 104. The example set of subcarriers A 102 includessubcarriers 103 and subcarriers 104. FIG. 1 also illustrates an exampleset of subcarriers B 105. As illustrated, there is no guard band betweenany two subcarriers in the example set of subcarriers B 105. Carriers ina multicarrier OFDM communication system may be contiguous carriers,non-contiguous carriers, or a combination of both contiguous andnon-contiguous carriers.

FIG. 2 is a diagram depicting an example transmission time and receptiontime for two carriers as per an aspect of an embodiment of the presentinvention. A multicarrier OFDM communication system may include one ormore carriers, for example, ranging from 1 to 10 carriers. Carrier A 204and carrier B 205 may have the same or different timing structures.Although FIG. 2 shows two synchronized carriers, carrier A 204 andcarrier B 205 may or may not be synchronized with each other. Differentradio frame structures may be supported for FDD (frequency divisionduplex) and TDD (time division duplex) duplex mechanisms. FIG. 2 showsan example FDD frame timing. Downlink and uplink transmissions may beorganized into radio frames 201. In this example, radio frame durationis 10 msec. Other frame durations, for example, in the range of 1 to 100msec may also be supported. In this example, each 10 ms radio frame 201may be divided into ten equally sized sub-frames 202. Other subframedurations such as including 0.5 msec, 1 msec, 2 msec, and 5 msec mayalso be supported. Sub-frame(s) may consist of two or more slots 206.For the example of FDD, 10 subframes may be available for downlinktransmission and 10 subframes may be available for uplink transmissionsin each 10 ms interval. Uplink and downlink transmissions may beseparated in the frequency domain. Slot(s) may include a plurality ofOFDM symbols 203. The number of OFDM symbols 203 in a slot 206 maydepend on the cyclic prefix length and subcarrier spacing.

In an example case of TDD, uplink and downlink transmissions may beseparated in the time domain. According to some of the various aspectsof embodiments, each 10 ms radio frame may include two half-frames of 5ms each. Half-frame(s) may include eight slots of length 0.5 ms andthree special fields: DwPTS (Downlink Pilot Time Slot), GP (GuardPeriod) and UpPTS (Uplink Pilot Time Slot). The length of DwPTS andUpPTS may be configurable subject to the total length of DwPTS, GP andUpPTS being equal to 1 ms. Both 5 ms and 10 ms switch-point periodicitymay be supported. In an example, subframe 1 in all configurations andsubframe 6 in configurations with 5 ms switch-point periodicity mayinclude DwPTS, GP and UpPTS. Subframe 6 in configurations with 10 msswitch-point periodicity may include DwPTS. Other subframes may includetwo equally sized slots. For this TDD example, GP may be employed fordownlink to uplink transition. Other subframes/fields may be assignedfor either downlink or uplink transmission. Other frame structures inaddition to the above two frame structures may also be supported, forexample in one example embodiment the frame duration may be selecteddynamically based on the packet sizes.

FIG. 3 is a diagram depicting OFDM radio resources as per an aspect ofan embodiment of the present invention. The resource grid structure intime 304 and frequency 305 is illustrated in FIG. 3. The quantity ofdownlink subcarriers or resource blocks (RB) (in this example 6 to 100RBs) may depend, at least in part, on the downlink transmissionbandwidth 306 configured in the cell. The smallest radio resource unitmay be called a resource element (e.g. 301). Resource elements may begrouped into resource blocks (e.g. 302). Resource blocks may be groupedinto larger radio resources called Resource Block Groups (RBG) (e.g.303). The transmitted signal in slot 206 may be described by one orseveral resource grids of a plurality of subcarriers and a plurality ofOFDM symbols. Resource blocks may be used to describe the mapping ofcertain physical channels to resource elements. Other pre-definedgroupings of physical resource elements may be implemented in the systemdepending on the radio technology. For example, 24 subcarriers may begrouped as a radio block for a duration of 5 msec.

Physical and virtual resource blocks may be defined. A physical resourceblock may be defined as N consecutive OFDM symbols in the time domainand M consecutive subcarriers in the frequency domain, wherein M and Nare integers. A physical resource block may include M×N resourceelements. In an illustrative example, a resource block may correspond toone slot in the time domain and 180 kHz in the frequency domain (for 15KHz subcarrier bandwidth and 12 subcarriers). A virtual resource blockmay be of the same size as a physical resource block. Various types ofvirtual resource blocks may be defined (e.g. virtual resource blocks oflocalized type and virtual resource blocks of distributed type). Forvarious types of virtual resource blocks, a pair of virtual resourceblocks over two slots in a subframe may be assigned together by a singlevirtual resource block number. Virtual resource blocks of localized typemay be mapped directly to physical resource blocks such that sequentialvirtual resource block k corresponds to physical resource block k.Alternatively, virtual resource blocks of distributed type may be mappedto physical resource blocks according to a predefined table or apredefined formula. Various configurations for radio resources may besupported under an OFDM framework, for example, a resource block may bedefined as including the subcarriers in the entire band for an allocatedtime duration.

According to some of the various aspects of embodiments, an antenna portmay be defined such that the channel over which a symbol on the antennaport is conveyed may be inferred from the channel over which anothersymbol on the same antenna port is conveyed. In some embodiments, theremay be one resource grid per antenna port. The set of antenna port(s)supported may depend on the reference signal configuration in the cell.Cell-specific reference signals may support a configuration of one, two,or four antenna port(s) and may be transmitted on antenna port(s) {0},{0, 1}, and {0, 1, 2, 3}, respectively. Multicast-broadcast referencesignals may be transmitted on antenna port 4. Wireless device-specificreference signals may be transmitted on antenna port(s) 5, 7, 8, or oneor several of ports {7, 8, 9, 10, 11, 12, 13, 14}. Positioning referencesignals may be transmitted on antenna port 6. Channel state information(CSI) reference signals may support a configuration of one, two, four oreight antenna port(s) and may be transmitted on antenna port(s) 15, {15,16}, {15, . . . , 18} and {15, . . . , 22}, respectively. Variousconfigurations for antenna configuration may be supported depending onthe number of antennas and the capability of the wireless devices andwireless base stations.

According to some embodiments, a radio resource framework using OFDMtechnology may be employed. Alternative embodiments may be implementedemploying other radio technologies. Example transmission mechanismsinclude, but are not limited to: CDMA, OFDM, TDMA, Wavelet technologies,and/or the like. Hybrid transmission mechanisms such as TDMA/CDMA, andOFDM/CDMA may also be employed.

FIG. 4 is an example block diagram of a base station 401 and a wirelessdevice 406, as per an aspect of an embodiment of the present invention.A communication network 400 may include at least one base station 401and at least one wireless device 406. The base station 401 may includeat least one communication interface 402, at least one processor 403,and at least one set of program code instructions 405 stored innon-transitory memory 404 and executable by the at least one processor403. The wireless device 406 may include at least one communicationinterface 407, at least one processor 408, and at least one set ofprogram code instructions 410 stored in non-transitory memory 409 andexecutable by the at least one processor 408. Communication interface402 in base station 401 may be configured to engage in communicationwith communication interface 407 in wireless device 406 via acommunication path that includes at least one wireless link 411.Wireless link 411 may be a bi-directional link. Communication interface407 in wireless device 406 may also be configured to engage in acommunication with communication interface 402 in base station 401. Basestation 401 and wireless device 406 may be configured to send andreceive data over wireless link 411 using multiple frequency carriers.According to some of the various aspects of embodiments, transceiver(s)may be employed. A transceiver is a device that includes both atransmitter and receiver. Transceivers may be employed in devices suchas wireless devices, base stations, relay nodes, and/or the like.Example embodiments for radio technology implemented in communicationinterface 402, 407 and wireless link 411 are illustrated are FIG. 1,FIG. 2, and FIG. 3. and associated text.

FIG. 5 is a block diagram depicting a system 500 for transmitting datatraffic generated by a wireless device 502 to a server 508 over amulticarrier OFDM radio according to one aspect of the illustrativeembodiments. The system 500 may include a Wireless CellularNetwork/Internet Network 507, which may function to provide connectivitybetween one or more wireless devices 502 (e.g., a cell phone, PDA(personal digital assistant), other wirelessly-equipped device, and/orthe like), one or more servers 508 (e.g. multimedia server, applicationservers, email servers, or database servers) and/or the like.

It should be understood, however, that this and other arrangementsdescribed herein are set forth for purposes of example only. As such,those skilled in the art will appreciate that other arrangements andother elements (e.g., machines, interfaces, functions, orders offunctions, etc.) may be used instead, some elements may be added, andsome elements may be omitted altogether. Further, as in mosttelecommunications applications, those skilled in the art willappreciate that many of the elements described herein are functionalentities that may be implemented as discrete or distributed componentsor in conjunction with other components, and in any suitable combinationand location. Still further, various functions described herein as beingperformed by one or more entities may be carried out by hardware,firmware and/or software logic in combination with hardware. Forinstance, various functions may be carried out by a processor executinga set of machine language instructions stored in memory.

As shown, the access network may include a plurality of base stations503 . . . 504. Base station 503 . . . 504 of the access network mayfunction to transmit and receive RF (radio frequency) radiation 505 . .. 506 at one or more carrier frequencies, and the RF radiation mayprovide one or more air interfaces over which the wireless device 502may communicate with the base stations 503 . . . 504. The user 501 mayuse the wireless device (or UE: user equipment) to receive data traffic,such as one or more multimedia files, data files, pictures, video files,or voice mails, etc. The wireless device 502 may include applicationssuch as web email, email applications, upload and ftp applications, MMS(multimedia messaging system) applications, or file sharingapplications. In another example embodiment, the wireless device 502 mayautomatically send traffic to a server 508 without direct involvement ofa user. For example, consider a wireless camera with automatic uploadfeature, or a video camera uploading videos to the remote server 508, ora personal computer equipped with an application transmitting traffic toa remote server.

One or more base stations 503 . . . 504 may define a correspondingwireless coverage area. The RF radiation 505 . . . 506 of the basestations 503 . . . 504 may carry communications between the WirelessCellular Network/Internet Network 507 and access device 502 according toany of a variety of protocols. For example, RF radiation 505 . . . 506may carry communications according to WiMAX (Worldwide Interoperabilityfor Microwave Access e.g., IEEE 802.16), LTE (long term evolution),microwave, satellite, MMDS (Multichannel Multipoint DistributionService), Wi-Fi (e.g., IEEE 802.11), Bluetooth, infrared, and otherprotocols now known or later developed. The communication between thewireless device 502 and the server 508 may be enabled by any networkingand transport technology for example TCP/IP (transport controlprotocol/Internet protocol), RTP (real time protocol), RTCP (real timecontrol protocol), HTTP (Hypertext Transfer Protocol) or any othernetworking protocol.

According to some of the various aspects of embodiments, an LTE networkmay include many base stations, providing a user plane (PDCP: packetdata convergence protocol/RLC: radio link control/MAC: media accesscontrol/PHY: physical) and control plane (RRC: radio resource control)protocol terminations towards the wireless device. The base station(s)may be interconnected with other base station(s) by means of an X2interface. The base stations may also be connected by means of an S1interface to an EPC (Evolved Packet Core). For example, the basestations may be interconnected to the MME (Mobility Management Entity)by means of the S1-MME interface and to the Serving Gateway (S-GW) bymeans of the S1-U interface. The S1 interface may support a many-to-manyrelation between MMEs/Serving Gateways and base stations. A base stationmay include many sectors for example: 1, 2, 3, 4, or 6 sectors. A basestation may include many cells, for example, ranging from 1 to 50 cellsor more. A cell may be categorized, for example, as a primary cell orsecondary cell. When carrier aggregation is configured, a wirelessdevice may have one RRC connection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell may providethe NAS (non-access stratum) mobility information (e.g. TAI-trackingarea identifier), and at RRC connection re-establishment/handover, oneserving cell may provide the security input. This cell may be referredto as the Primary Cell (PCell). In the downlink, the carriercorresponding to the PCell may be the Downlink Primary Component Carrier(DL PCC), while in the uplink, it may be the Uplink Primary ComponentCarrier (UL PCC). Depending on wireless device capabilities, SecondaryCells (SCells) may be configured to form together with the PCell a setof serving cells. In the downlink, the carrier corresponding to an SCellmay be a Downlink Secondary Component Carrier (DL SCC), while in theuplink, it may be an Uplink Secondary Component Carrier (UL SCC). AnSCell may or may not have an uplink carrier.

A cell, comprising a downlink carrier and optionally an uplink carrier,is assigned a physical cell ID and a cell index. A carrier (downlink oruplink) belongs to only one cell, the cell ID or Cell index may alsoidentify the downlink carrier or uplink carrier of the cell (dependingon the context it is used). In the specification, cell ID may be equallyreferred to a carrier ID, and cell index may be referred to carrierindex. In implementation, the physical cell ID or cell index may beassigned to a cell. Cell ID may be determined using the synchronizationsignal transmitted on a downlink carrier. Cell index may be determinedusing RRC messages. For example, when the specification refers to afirst physical cell ID for a first downlink carrier, it may mean thefirst physical cell ID is for a cell comprising the first downlinkcarrier. The same concept may apply to, for example, carrier activation.When the specification indicates that a first carrier is activated, itequally means that the cell comprising the first carrier is activated.

Embodiments may be configured to operate as needed. The disclosedmechanism may be performed when certain criteria are met, for example,in wireless device, base station, radio environment, network, acombination of the above, and/or the like. Example criteria may bebased, at least in part, on for example, traffic load, initial systemset up, packet sizes, traffic characteristics, a combination of theabove, and/or the like. When the one or more criteria are met, theexample embodiments may be applied. Therefore, it may be possible toimplement example embodiments that selectively implement disclosedprotocols.

Example embodiments of the invention may enable beamforming informationto be exchanged between base stations. Other example embodiments maycomprise a non-transitory tangible computer readable media comprisinginstructions executable by one or more processors to cause beamforminginformation to be exchanged between base stations. Yet other exampleembodiments may comprise an article of manufacture that comprises anon-transitory tangible computer readable machine-accessible mediumhaving instructions encoded thereon for enabling programmable hardwareto cause a device (e.g. wireless communicator, user equipment (UE), basestation, etc.) to exchange beamforming information between basestations. The device may include processors, memory, interfaces, and/orthe like. Other example embodiments may comprise communication networkscomprising devices such as base stations, wireless devices (or UE),servers, switches, antennas, and/or the like.

According to some of the various aspects of embodiments, base stationsin a wireless network may be directly or indirectly connected to eachother to exchange signaling and data packets. This interface in LTE andLTE-Advanced may be called an X2 interface. Other embodiments of theinterface may also possible, for example, using an S1 interface. The X2user plane interface (X2-U) may be defined between base stations. TheX2-U interface may provide non-guaranteed delivery of user plane packetdate units (PDUs). The transport network layer may be built on internetprotocol (IP) transport and GPRS tunneling protocol user plane (GTP-U)may be used on top of user datagram protocol (UDP)/IP to carry the userplane PDUs. The X2 control (X2-C) plane interface may be defined betweentwo neighbor base stations. The transport network layer may be built onStream Control Transmission Protocol (SCTP) on top of IP. Theapplication layer signaling protocol may be referred to as X2Application Protocol (X2-AP). A single SCTP association per X2-Cinterface instance may be used with one pair of stream identifiers forX2-C common procedures. A few pairs of stream identifiers may be usedfor X2-C dedicated procedures. The list of functions on the interfacebetween the base stations may include the following: mobility support,load management, inter-cell interference coordination, and dataexchange.

In order to establish an association between two base stations, a firstbase station sends a first message to a second base station to initiatean association between two endpoints. The first initiation message maycomprise multiple parameters such as the following: initiate tag,advertised receiver window credit, number of outbound streams, number ofinbound streams, an initial transmit sequence number, a combinationthereof, and/or the like.

According to some of the various aspects of the embodiments, aninitiation tag may be a 32-bits unsigned integer. The receiver of theinitiation message (the responding end) may record the value of theinitiate tag parameter. This value may be placed into the verificationtag field of SCTP packet(s) that the receiver of the initiation messagetransmits within this association. In an example, the initiation tag maybe allowed to have any value except zero.

According to some of the various aspects of the embodiments, theadvertised receiver window credit may be a 32-bit unsigned integer. Thesender of the initiation message may reserve a dedicated buffer spacedefined by the number of bytes in association with this window. Duringthe life of the association, the size of this buffer space may bemaintained (e.g., dedicated buffers taken away from this association);however, an endpoint may change the value of window credit it sends in apacket. The number of outbound streams may be represented by a 16-bitunsigned integer which may define the number of outbound streams thesender of the initiation message wishes to create during an association.The number of inbound streams may be represented by a 16-bit unsignedinteger and may define the maximum number of streams the sender of theinitiation message may allow the peer end to create during theassociation between the two base stations. The two endpoints may use theminimum of requested and offered parameters rather than negotiation ofthe actual number of streams. The initial transmit sequence number maybe represented by a 32-bit unsigned integer and may define the initialtransmit sequence number that the sender may use. This field, forexample, may be set to the value of the initiate tag field.

According to some of the various aspects of embodiments, the second basestation may transmit an initiation acknowledgement message toacknowledge the initiation of an SCTP association with the first basestation. The parameter part of the initiation acknowledgement messagemay be formatted similarly to the initiation message. The parameter partof the initiation acknowledgement message may use two extra variableparameters: the state cookie and the unrecognized parameter. Theinitiate tag may be represented by a 32-bit unsigned integer. Thereceiver of the initiation acknowledgement message may record the valueof the initiate tag parameter. This value may be placed into theverification tag field of SCTP packet(s) that the initiationacknowledgement message receiver transmits within this association.According to some of the various aspects of the embodiments, theadvertised receiver window credit may represented by a 32-bit unsignedinteger. This value may represent the dedicated buffer space, in termsof the number of bytes, that the sender of the initiationacknowledgement message has reserved in association with this window.During the life of the association, the size of this buffer space may bemaintained (e.g. not be lessened or taken away from this association).

According to some of the various aspects of embodiments, the number ofoutbound streams may be represented by, for example, a 16-bit unsignedinteger. The number of outbound streams may define the number ofoutbound streams the sender of the initiation acknowledgement messagewishes to create during this association between base stations. Thenumber of inbound streams may, for example, be a represented in terms ofa 16-bit unsigned integer. It may define the maximum number of streamsthe sender of this initiation acknowledgement message allows the peerend to create. The two endpoints may use the minimum of requested andoffered parameters, rather than negotiation of the actual number ofstreams. An initial transmit sequence number (TSN) may be a representedby a 32-bit unsigned integer. The initial transmit sequence number (TSN)may define the initial TSN that the initiation acknowledgement messagesender may use. This field may be set to the value of the initiate tagfield. The state cookie parameter may contain the needed state andparameter information required for the sender of this initiationacknowledgement message to create the association between base stations.The state cookie parameter may also include a message authenticationcode (MAC). An unrecognized parameter may be returned to the originatorof the initiation message when the initiation message contains anunrecognized parameter that has a value that indicates it should bereported to the sender. This parameter value field may containunrecognized parameters copied from the initiation message completewith, for example, parameter type, length, and value fields.

According to some of the various aspects of embodiments, when sending aninitiation acknowledgement message as a response to an initiationmessage, the sender of the initiation acknowledgement message may createa state cookie and send it in the state cookie parameter of theinitiation acknowledgement message. Inside this state cookie, the sendermay include a message authentication code, a timestamp on when the statecookie is created, and the lifespan of the state cookie, along with theinformation needed for it to establish the association. The followingsteps may be taken to generate the state cookie: 1) Create anassociation transmission control block (TCB) using information from boththe received initiation message and the outgoing initiationacknowledgement messages, 2) In the TCB, set the creation time to thecurrent time of day, and the lifespan to the protocol parameter to apre-determined number, 3) From the TCB, identify and collect the minimalsubset of information needed to re-create the TCB, and generate a MACusing this subset of information and a secret key, and/or 4) Generatethe state cookie by combining this subset of information and theresultant MAC.

After sending the initiation acknowledgement with the state cookieparameter, the sender may delete the TCB and any other local resourcerelated to the new association so as to prevent resource attacks. Thehashing method used to generate the MAC may be strictly a private matterfor the receiver of the initiation message. The MAC may be used toprevent denial-of-service attacks. The secret key may be random. Thesecret key may be changed reasonably frequently, and the timestamp inthe state cookie may be used to determine which key should be used toverify the MAC. An implementation of an embodiment may make the cookieas small as possible to ensure interoperability.

According to some of the various aspects of embodiments, the first basestation may transmit at least one third message to the second basestation. One of the at least one third message may be a cookie-echomessage. The cookie-echo message may be used during the initializationof an association. It may be sent by the initiator of an association toits peer to complete the initialization process. This cookie-echomessage may precede any transport packet message sent within theassociation and may be bundled with one or more data transport packet inthe same packet. This message may contain the cookie received in thestate cookie parameter from the previous initiation acknowledgementmessage. The type and flags of the cookie-echo may be different than thecookie parameter. Some embodiments may make the cookie as small aspossible to ensure interoperability. A cookie echo may not contain astate cookie parameter, but instead, the data within the state cookie'sparameter value becomes the data within the cookie echo's chunk value.This may allow an implementation of an embodiment to change the firsttwo bytes of the state cookie parameter to become a cookie echo message.The first base station may transmit at least one application protocolmessage in the cookie echo message. Alternatively, an implementationoption may be for the base station to transmit application protocolmessages after the association is complete and to not includeapplication protocol messages in a cookie-echo message.

The application protocol message may receive a cookie-ack message fromthe second base station. This application protocol message may be usedduring the initialization of an association. The application protocolmessage may also be used to acknowledge the receipt of a cookie-echomessage. This application protocol message may precede other data sentwithin the association and may be bundled with one or more data packetsin the same SCTP packet. The second base station may transmit at leastone application protocol message in a cookie ack message. Alternatively,according to one embodiment, the base station may choose to transmitapplication protocol messages after the association is complete ratherthan include application protocol messages in a cookie-ack message.

After the initiation and initiation acknowledgement messages aretransmitted, the first base station or the second base station maytransmit an X2 setup message to cause an X2 application interface to beconfigured. The first base station or the second base station may waituntil the association is complete to set up an X2 application interface.Either the first base station or second base station could start thesetup of the X2 application. The purpose of an X2 setup procedure couldbe to exchange application level configuration data needed for two basestations to interoperate correctly over the X2 interface. This proceduremay erase any existing application level configuration data in the twonodes and replace the application level configuration data by the onereceived by the X2 setup message. This procedure may also reset the X2interface.

A first base station or second base station may initiate the X2 setupprocedure by sending the X2 set up request message to a candidate basestation. The candidate base station may reply with the X2 set upresponse message. The initiating base station may transfer the list ofserved cells. The candidate base station may reply with the completelist of its served cells.

FIG. 11 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention.According to some of the various aspects of embodiments, a base stationmay receive a first application protocol message, for example an X2 setup request message, as shown in 1101. The X2 set up request message mayinclude the following information about the originator of the message: aglobal base station identifier, the information about the served cells,and a group identifier list. The group identifier list identifies thepools to which the base station belongs to. Each row in this list mayinclude the public land mobile network (PLMN) ID and mobility managemententity (MME) group identifier. The information about each served cellmay include information about the served cell configurations and mayalso include the list of neighbor cells of the served cell including,for example: the cell global identifier of the neighbor cell, thephysical cell identifier of the neighbor cell, and the frequency of thecells. The served cell information may include at least one of thefollowing parameters: a physical cell ID, a global cell identifier, atracking area code, at least one broadcast PLMN, frequency divisionduplexing (FDD) information (uplink and downlink frequencies, uplink anddownlink transmission bandwidth), time division duplexing (TDD)information (transmission frequency, subframe assignment, specialsubframe information, special subframe pattern, cyclic prefix fordownlink and uplink), number of antenna ports, physical random accesschannel (PRACH) configuration, multicast broadcast single frequencynetwork (MBSFN) subframe info (radio frame allocation period, radioframe allocation offset, subframe allocation), and a CSG identifier. TheX2 set up request or some other subsequent application protocol messagesmay also include a beamforming codebook comprising a plurality ofbeamforming codewords. Each of the plurality of beamforming codewordsmay be identifiable by an index. In an example implementation, thecodebook may be transmitted in the form of a look up table includingrows, columns, and/or the like. For example, each row may include theindex and the codeword corresponding to that index. A codeword in a rowmay be identifiable by the index in the same row. In another exampleimplementation, the codewords in a codebook may be ordered according totheir index. Identifying a codeword by an index may be performedimplicitly according to codeword order or codeword ranking in a list.The indexes may or may not be included in the message transmitted on theX2 interface. The index(es) may be employed in other messages in orderto refer to the codeword. In an example implementation, rows could beimplemented as columns by just transposing the implemented matrix orarray. It is also possible to implement a matrix, rows and/or columns ofvariables using various techniques such as using pointers, objectoriented programming structures or other various programming structuresconfigured to store a list of interrelated variables.

The index may be presented by a number of bits in a transmitted messagebetween base stations or between a base station and a wireless device.The number of bits may be greater than or equal to log₂(N), N being thenumber of the plurality of beamforming codewords. The number of bits maybe less than the number of bits in a corresponding beamforming codeword.

The first base station may receive at least one fourth message from asecond base station. The at least one fourth message may comprise asecond beamforming codebook comprising a second plurality of codewords.The base station may receive from a second base station, at least onesecond application protocol message comprising at least one index in theplurality of indexes as shown in 1102. The at least one index mayidentify a subset of the plurality of beamforming codewords. The firstbase station may transmit signals to a plurality of wireless devicesemploying a first plurality of beamforming codewords from a firstbeamforming codebook as shown in 1103. The first plurality of codewordsmay be selected, at least in part, employing the subset of the secondplurality of beamforming codewords.

The base station may transmit signals (data and/or control packets) to aplurality of wireless devices using a first plurality of beamformingcodewords from a first beamforming codebook. The first plurality ofcodewords may be selected based, at least in part, on informationreceived from the other base station. The information may compriseindexes of codewords from the second beamforming codebook. In some ofthe various embodiments, a first base station may transmit X2 messagesto cause configuration of a table of codewords in a second base station.The first base station may then refer to the index(es) in the sameand/or subsequent messages to refer to a codeword(s). The process mayreduce the number of bits transmitted on the X2 and/or air interfaces.In an example embodiment, a codebook may include ten codewords. (N=10).Each codeword may be a variable presented by fifty bits. The indexes maybe presented by k number of bits, k being a number greater than or equalto four and less than fifty.

According to some of the various aspects of embodiments, a first basestation may transmit a first message to initiate an association betweenthe first base station and a second base station in the plurality ofbase stations. The first message may comprise a first initiation tag.The first base station may receive a second message from the second basestation. The second message may comprise a second verification tag, asecond initiation tag, and a first state parameter. The secondverification tag may be equal to the first initiation tag. A first stateparameter may comprise at least one parameter related to operationalinformation of the association and a message authentication codegenerated as a function of a private key.

The first base station may transmit at least one third message to thesecond base station. The at least one third message may comprise a firstverification tag, a parameter, and a first application protocol message.The first verification tag may be equal to the second initiation tag.The parameter may comprise the first state parameter. The firstapplication protocol message may comprise a unique identifier of thefirst base station, at least one MME group identifier, and a firstbeamforming codebook. The first beamforming codebook may comprise afirst plurality of beamforming codewords. Each of the first plurality ofbeamforming codewords may be identifiable by an index. The index may bepresented by a number of bits. The number of bits may be greater than orequal to log₂(N), wherein N is the number of the plurality ofbeamforming codewords. The number of bits may be smaller than the numberof bits in a corresponding beamforming codeword. The first base stationmay receive at least one fourth message from the second base stationcomprising an acknowledgement for the receipt of the parameter. Thesecond base station may transmit signals to a plurality of wirelessdevices using a second plurality of beamforming codewords from a secondbeamforming codebook. The first plurality of codewords may be selectedbased, at least in part, on information received from the first basestation. The information may comprise indices of codewords from saidfirst beamforming codebook.

FIG. 10 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention.According to some of the various aspects of embodiments, a first basestation may transmit a first message to initiate an association betweenthe first base station and a second base station in the plurality ofbase stations as shown in 1001. The first message may comprise a firstinitiation tag. The first base station may receive a second message fromthe second base station as shown in 1002. The second message maycomprise: a second verification tag, a second initiation tag, a firststate parameter, a combination thereof, and/or the like. The secondverification tag may be equal to the first initiation tag. The firststate parameter may comprise at least one parameter related tooperational information of the association, and a message authenticationcode generated as a function of a private key. The first base stationmay transmit at least one third message to the second base station asshown in 1003. The at least one third message may comprise a firstverification tag and a parameter. The first verification tag may beequal to the second initiation tag. The parameter may comprise the firststate parameter.

The first base station may receive at least one fourth message from thesecond base station as shown in 1004. The at least one fourth messagemay comprise an acknowledgement for the receipt of the parameter, and asecond application protocol message. The second application protocolmessage may comprise a unique identifier of the second base station, atleast one MME group identifier, and a second beamforming codebook. Thesecond beamforming codebook may comprise a second plurality ofbeamforming codewords. Each of the second plurality of beamformingcodewords may be identifiable by an index. The index may be presented bya number of bits. The number of bits may be greater than or equal tolog₂(N), wherein N is the number of the plurality of beamformingcodewords. The number of bits may be smaller than the number of bits ina corresponding beamforming codeword. The first base station maytransmit signals to a plurality of wireless devices using a firstplurality of beamforming codewords from a first beamforming codebook asshown in 1006. The first plurality of codewords may be selected based,at least in part, on information received from the second base stationas shown in 1005. The information may comprise indices of codewords fromthe second beamforming codebook.

According to some of the various aspects of embodiments, the firstinitiation tag value may be selected in the first base station using apseudo-random process. The second initiation tag value may be selectedin the second base station using a pseudo-random process. The firstmessage may further comprise a first base station transport address anda second base station transport address. The first message may furthercomprise a first advertised receiver window credit representing adedicated buffer space that the first base station reserves for a windowof received packets from the second base station. The first message mayfurther comprise a first initial transmission sequence number that thefirst base station uses for transmission of data segments. The firstinitial transmission sequence number may be equal to the firstinitiation tag.

The second message may further comprise the first base station transportaddress and the second base station transport address. The secondmessage may further comprise a second advertised receiver window creditrepresenting a dedicated buffer space that the second base stationreserves for a window of received packets from the first base station.The second message may further comprise a second initial transmissionsequence number that the second base station uses for transmission ofdata chunks. The second initial transmission sequence number may beequal to the second initiation tag. The at least one third message mayfurther comprise the first base station transport address and the secondbase station transport address. The at least one third message mayfurther comprise a transmit sequence number, a stream identifier, astream sequence number.

The at least one fourth message may further comprise a transmit sequencenumber, a stream identifier, and a stream sequence number. The secondbase station may place the first initiation tag in the verification tagof every transport layer packet that it transmits to the first basestation within the association. The first base station may place thesecond initiation tag in the verification tag of every SCTP packet thatit transmits to the second base station within the association. Theassociation may be an SCTP association. The at least one fourth messagemay further comprise the first base station transport address and thesecond base station transport address. The second application protocolmessage may be an X2-Application Protocol Setup Request message. Thesecond application protocol message may be an X2-Application ProtocolSetup Response message. The at least one third message may furthercomprise an X2-Application Protocol Setup Request message. The at leastone third message may further comprise an X2-Application Protocol SetupResponse message.

The first state parameter may further comprise a timestamp on when thefirst state parameter is created. The first state parameter may furthercomprise the lifespan of the first state parameter. The messageauthentication code may further be a function of at least one parameterrelated to operational information of the association. The at least onethird message may further comprise a first application protocol message.The first application protocol message may comprise a unique identifierof the first base station, at least one MME group identifier, abeamforming codebook comprising a first plurality of beamformingcodewords. Each of the first plurality of beamforming codewords may beidentifiable by an index. The index may be presented by the first numberof bits.

The first verification tag and the second verification tag in theassociation may not change during the life time of the association. Anew verification tag value may be used each time the first base stationor the second base station tears down and then reestablishes anassociation with the same node. The operational information may compriseat least one of the following: a parameter in the first message, aparameter in the second message, a state of the association, aconfiguration parameter of the first base station, a configurationparameter of the second base station, a combination thereof, and/or thelike. The first message and the second message may further comprise achecksum for packet validation. The first base station transport addressand the second base station transport address may comprise an IP addressand a port address.

The first message may further comprise a first number of outboundstreams that the first base station intend to create and a first maximumnumber of inbound streams that the first base station allows the secondbase station to create. The second message may further comprise a secondnumber of outbound streams that the second base station intend tocreate, a second maximum number of inbound streams the second basestation allows the first base station to create. The second number ofoutbound streams is smaller than or equal to the first maximum number ofinbound streams. The first base station may further select a numberequal or lower than the minimum of the first number of outbound streamsand the second maximum number of inbound streams as the number ofoutbound streams for the first base station.

The first base station may use the plurality of indexes incommunications with the second base station. Each of the plurality ofindexes may refer to a locally unique beamforming codeword. The secondapplication protocol message may further comprise the number of antennasof each cell in the second base station. The second application protocolmessage may further comprise a cell ID for each cell in the second basestation. The second application protocol message may further comprisethe frequency of each downlink and uplink carrier of the second basestation. The first beamforming codebook and second beamforming codebookmay be the same. The first plurality of beamforming codewords may beselected to reduce inter-cell interference from the second base station.The first base station may use information received from at least onewireless device to compute the inter-cell interference from the secondbase station.

The first plurality of beamforming codewords may be selected to reduceinter-cell interference to the second base station. The first basestation may use information received from at least one wireless deviceto compute the inter-cell interference to the second base station. Thefirst beamforming codebook or the second beamforming codebook may bedefined for a maximum number of transmit antennas and comprises a set oforiginal codewords. Each original codeword may have a number of rows orcolumns equal to the maximum number of transmit antennas. Codewords fora smaller number of transmit antennas may be constructed by using asubset of rows or columns of the original codewords. The firstbeamforming codebook or the second beamforming codebook may be definedfor a maximum number of layers and may comprise a set of codewords. Eachcodeword may have a number rows or columns equal to the maximum numberof layers. Codewords for a smaller number of layers may be constructedby using a subset of columns or rows of the original codewords.

The first base station may exchange similar messages with a plurality ofsecond base stations. The first plurality of beamforming codewords maybe selected to reduce inter-cell interference from a subset of theplurality of second base stations. The first base station may useinformation received from at least one wireless device to compute theinter-cell interference from the subset of the plurality of second basestations. The first plurality of beamforming codewords may be selectedto reduce inter-cell interference to a subset of the plurality of secondbase stations. The first base station may use information received fromat least one wireless device to compute the inter-cell interference tothe subset of the plurality of second base stations. The second basestation may transmit the same second application protocol message to aplurality of first base stations. The plurality of first base stationsmay select their respective first plurality of beamforming codewordsbased on information received from the second base station in the secondapplication protocol message.

FIG. 6 is a block diagram of a limited feedback system according to anaspect of an embodiment of the present invention. Wireless device 604measures information about a wireless channel (either perfect orimperfect) between the base station 602 transmitter and the wirelessdevice 604 receiver. This receiver channel information may be fed into aquantizer/encoder 605 that returns a small number of feedback bits to besent as overhead on reverse link 606. The base station 602 transmittermay use the received feedback bits to adapt the transmitted signal toforward channel 607.

The limited feedback may be implemented in multiple antenna wirelesssystems. Limited feedback may be a viable and beneficial option for asystem that adapts a spatial degree-of-freedom. The degrees of freedomwith multiple antenna systems may be exploited to offer rate anddiversity benefits as well as beamforming and interference cancelingcapabilities. While the diversity gain may be extracted without the needof channel state information at the transmitter (CSIT) feedback (e.g.,space time codes), CSIT may play a role for beamforming and interferencemitigation at the transmitter.

A single-user narrowband multiple antenna system may be represented byan expression of the form y[k]=H[k]x[k]+n[k] at the k-th channel.Assuming M_(t) transmit antennas and M_(r) receive antennas, y[k] may bean M_(r)-dimensional receive vector, H[k] may be an M_(r)×M_(t) channelresponse matrix, x[k] may be an M_(t)-dimensional transmit vector, andn[k] may be M_(r)-dimensional noise. The noise may be assumed to haveindependent and identically distributed (iid) normalized entriesdistributed according to CN(0, 1). As in the single antenna case, thescenario where the receiver has access to H[k] may be considered. Giventhis, there may be a variety of ways to design x[k] if the transmitteris given access to some quantized information relating to H[k]. Again,this analysis may depend on the time evolution model of the channel. Ifwe use notation of block-fading, the tth channel block may satisfyH[tKch]=H[tKch+1]= . . . =H[(t+1)Kch−1]=H(t) where Kch is the length ofthe fading block.

When the transmitter and receiver both know the channel, the ergodiccapacity may be

R = E_(H)[_(Q : tr(Q) ≤ 1, Q^(*) = Q, Q ≥ 0)det (I + ρ HQH^(*))].

Here, Q may be the covariance of the transmitted signal for eachindividual instantaneous channel realization. The covariance of thetransmitted signal may incorporate both the spatial power allocation aswell as unitary precoding. Spatial power allocation may be needed forcases when the number of transmit antennas is greater than the number ofreceive antennas. From an encoding point of view, x[k]=√{square rootover (ρ)}(Q[k])^(1/2)s[k], k=0, . . . , K_(bl)−1 where Q[k] may solvethe optimization (based on channel feedback)

Q[k] = _(Q : tr(Q) ≤ 1, Q^(*) = Q, Q ≥ 0)det (I + ρ HQH^(*)).

and s[k] may the k-th channel use of an open-loop codeword.

For a limited rate feedback approach, the general idea may be to use thefact that the receiver knows H[k] through procedures such as training.Using this channel knowledge, the receiver may quantize some function ofH[k] using vector quantization (VQ) techniques.

Naturally, the aspects of the channel that the transmitter cares aboutare those that allow the design of the covariance for the t^(th) channelblock. Using this line of reasoning, the receiver may determine a ratemaximizing covariance and feed this back to the transmitter. Employing acodebook of possible covariance matrices Q={Q₁, . . . , Q₂ _(B) } thatmay be known to the transmitter and receiver, the receiver may searchfor the codebook index.

The covariance codebook may be either fixed or randomly generated (usinga seed known to both the transmitter and receiver). Designing a fixedcovariance codebook to maximize the average rate may be a challengingproblem that depends on the stationary distribution of the channel.Vector quantization approaches may efficiently generate codebooks thatachieve a large rate. Random approaches for a covariance design may alsobe possible. The rate loss with B bits of feedback may decrease with thenumber of feedback bits.

While the codebook approach may be used for a block-to-blockindependently fading channel, temporal correlation between channelrealizations may improve quantization. Feedback approaches based ontracking the channel using gradient analysis may also be possible. Theuse of switched codebooks, where the codebook is changed or adapted overtime may be implemented. Orientation and radius of a localized codebookcap changing over time may be implemented with beamforming codebookswhich have adaptive localized codebook caps. Models may be used toimplement feedback compression. For example, Markov chain compressionmay be employed to analyze the effects of feedback delay and channeltime evolution.

In an example embodiment, beamforming may be characterized by the use ofa rank one covariance matrix. Using a rank one Q matrix may be usefulwhenever the single-user channel is itself rank one. This may occur whenthe user terminal is equipped with a single antenna. In this situation,the availability of CSIT may be needed.

In beamforming, the single-user multiple input multiple output (MIMO)expression in y[k]=H[k]x[k]+n[k] may be restricted so that x[k]=√{squareroot over (ρ)}f[k]s[k] where f[k] is a channel dependent vector referredto as a beamforming vector and s[k] is a single-dimensional complexsymbol chosen independently of instantaneous channel conditions. In themultiple input single output (MISO) case, there may be a single receiveantenna. In this case, y[k] may be reformulated as y[k]=√{square rootover (ρ)}h^(T)[k]f[k]s[k]+n[k]. h[k] may be a column vector. With thisconfiguration, the receive SNR at channel use k (averaged with respectto the transmitted signal and noise) may be given bySNR[k]=ρ|h^(T)[k]f[k]|².

For MIMO beamforming and combining, a receive-side combining vector z[k](sometimes, but not necessarily, unit norm) may be used so that afterprocessing y[k]=√{square root over (ρ)}z*[k]H[k]f[k]s[k]+z*[k]n[k].Conjugate transpose is denoted by *. Various forms of combiners may beimplemented.

The receiver may be allowed to send some feedback to assist thetransmitter's configuration. An example form of this feedback may selecta transmit antenna(s). In this scenario, the transmit beamforming vectormay be restricted such that one entry is non-zero. With this kind ofset-up in a MISO system, a solution may be to send data on the antennathat substantially maximizes the receiver SNR, meaning data (and power)may be sent on antenna

m_(opt)[k] = _(1 ≤ m ≤ M_(t))h_(m)[k]

h_(m)[k] may denote the m^(th) antenna entry of the channel vector h[k].Using this approach, the selected antenna may be configured at thereceiver and may be sent back to the transmitter using[log₂(M_(t))]bits. Error rates with antenna selection for spatiallyuncorrelated set-ups may be considered.

Antenna selection may be limited in terms of its benefits to the overallcapacity as it may not allow for the full beamforming gain. If thereexists a feedback link, more complicated forms of channel dependentfeedback may improve performance. The channel vector may be quantizedfor a MISO system into a set of normalized column vectors={h₁, . . . ,h₂ _(B) }. Because the system may have a single receive antenna, thechannel vector h[k] may be quantized over this set by selecting thecodebook vector h_(n) _(opt) [k] using a phase invariant distortion suchthat

n_(opt)[k] = _(1 ≤ m ≤ 2^(B))h_(n)^(*)h[k].

The transmitter can then pick a beamforming vector that solves

${f\lbrack k\rbrack} = {{{{}_{{f:{{f}}} = 1}^{}{}_{}^{}}\left( {1 + {\rho {{h_{n_{opt}{\lbrack k\rbrack}}^{T}f}}^{2}}} \right)} = {\frac{\left( h_{n_{opt}{\lbrack k\rbrack}}^{T} \right)^{*}}{{{h_{n_{opt}{\lbrack k\rbrack}}^{T}}}_{2}}.}}$

Equal gain approaches that attempt to co-phase the signals received fromvarious antennas may be implemented. This concept may be implemented toquantize the phases of each h_(m)[k], m=1, . . . , M_(t), using uniformphase quantization on a unit circle.

The codebooks may allow the receiver to directly configure thebeamforming vector and send this vector back to the transmitter. In oneexample embodiment, beamforming vector quantization may be consideredrather than channel quantization. f[k] may be restricted to lie in a setor codebook F={f₁, . . . , f₂ _(B) }. The receiver may use its channelknowledge to pick the required vector from the codebook.

This kind of approach is demonstrated in FIG. 7 using the interpretationthat beamforming may be rank one precoding. FIG. 7 is a block diagram ofa limited feedback linear precoded MIMO system according to anembodiment. The receiver 702 in wireless device 701 may use a channelestimate to pick the optimal transmitter-side linear precoder from acodebook known to the transmitter and receiver. The wireless device 701may use quantization 703 to calculate feedback. For a codebook of size2^(B), the B-bit binary label of the chosen precoder may be sent overfeedback channel 705 to base station 704. Note that the rate and/or SNRmay also be known as side information to facilitate communication andmay be fed back to the base station.

The receiver now, in some sense, may control how the signal is adaptedto the channel. Phase quantization codebooks may be implemented for MIMObeamforming and combining. This may jointly quantize the phases acrosstransmit antennas and implement diversity. While equal gain approachesmay be an option, a general design framework may be useful. Determiningfavorable configuration parameters for a spatially uncorrelated Rayleighfading channel may be a goal for outage minimizing, SNR maximizing, ratemaximizing, a combination thereof, and/or the like.

For a channel, the maximum diversity order may be when the rank of thematrix [f₁, . . . , f₂ _(B) ] constructed from the set of beamformingvectors has a rank of M_(t). Receiver SNR degradation may be analyzed.Insights from the problem of Grassmannian line packing designs may beused to assist analysis. Closed-form integral expressions may beobtained by modeling the feedback problem as one of a correlated antennaselection. An alternative approach to Grassmannian codebooks may be toconstruct the codebooks using vector quantization (VQ) techniques. Adistortion function (usually related to rate loss or SNR loss) may beformulated and the distortion function may be iteratively minimized toobtain local solutions. Using multiple iterations with different(possibly randomized) initial settings may yield an approximatelyoptimal codebook. Because of the unit vector constraints on thebeamforming vector set, this may be a problem in spherical vectorquantization. VQ designs also may have useful analytical properties whenthe codebook size (or quantizer resolution) increases. High resolutionanalysis and codebook design may be leveraged to give new insight intocodebook behavior.

Grassmannian and VQ limited feedback designs may assume codebooks thatare fixed and do not vary as the channel changes. Another implementationmay be to randomly generate the codebook at each block (with therandomly generated codebook known to both the transmitter and receiver).This sort of codebook design technique may be based on random vectorquantization (RVQ). The idea here is to generate the 2^(B) codebookvectors independently and all identically distributed according to thestationary distribution of the quantized beamforming vector.

For example, a MISO system with channel information at the transmitterand receiver may use a beamforming vector

${f\lbrack k\rbrack} = \frac{\left( {h^{T}\lbrack k\rbrack} \right)^{*}}{{{{h\lbrack k\rbrack}}}_{2}}$

(known as maximum ratio transmission). When the channel distribution isa spatially uncorrelated Rayleigh, the vector may follow a uniformdistribution on the unit sphere. Thus, the RVQ codebook may beconstructed by taking 2^(B) independently and uniformly generated pointson the unit sphere. These kinds of codebooks may have very asymptoticproperties as the number of antennas scales to infinity. Closed-formanalysis may also be possible when the channel follows a spatiallyuncorrelated Rayleigh model. Several other codebook designs may beconsidered as alternatives to Grassmannian line packings, vectorquantization, and RVQ. Equiangular frame based codebooks may beimplemented based on the observation that (in the real case) codebooksfrom equiangular frames maximize the mutual information between the truebeamforming vector and the quantized precoding vector. In certain casesGrassmannian line packing may lead to equiangular frames. Codebooks maybe generalized based on the Fourier concept for limited feedback. Thekey idea is to recognize that the non-coherent MIMO space-time codedesign problem may also be the problem of finding packings on theGrassmann manifold. DFT codebooks may introduce additional structure inFourier codebooks, further simplifying their design. Adaptive modulationmay be combined with beamforming codebooks. Techniques for dealing withtime variation of the channel during the feedback phase may beconsidered in an example implementation.

Fourth generation (4G) and beyond cellular standards may use MIMO-OFDMtechnology. Generalizing the input-output relation to MIMO for thev^(th) subcarrier yields {tilde over (y)}v [{tilde over (k)}]={tildeover (H)}v[{tilde over (k)}]{tilde over (X)}v[{tilde over(k)}]+ñv[{tilde over (k)}] for OFDM channel use {tilde over (k)}. In theformula, {tilde over (y)}v[{tilde over (k)}] is an M_(r)-dimensionalreceived signal for subcarrier v, {tilde over (H)}v[{tilde over (k)}] isan M_(r)×M_(t) channel realization (in the frequency domain) for thev^(th) subcarrier, {tilde over (x)}v[{tilde over (k)}] is anM_(t)-dimensional dimensional transmitted signal for subcarrier v, andñv[{tilde over (k)}] is M_(r)-dimensional normalized additive noise withiid CN(0, 1) entries.

MIMO channel adaptation may be done on a per-subcarrier basis. Forexample, a linear precoded spatial multiplexing system may set {tildeover (x)}v[{tilde over (k)}]=√{square root over (ρv)}{tilde over(F)}v[{tilde over (k)}]{tilde over (s)}v[{tilde over (k)}], where ρ_(v)is the SNR on subcarrier v, {tilde over (F)}v[{tilde over (k)}] is theM_(t)×M precoder on subcarrier v, and {tilde over (s)}v[{tilde over(k)}] is an M-dimensional transmitted spatial multiplexing vector. Theprecoder {tilde over (F)}v[{tilde over (k)}] may be adapted directly to{tilde over (H)}v[{tilde over (k)}].

MIMO-OFDM feedback systems may send feedback for pilot subcarriers v₀, .. . , v_(K) _(pilot) ⁻¹ where K_(pilot) is a function of the number ofpilots. For example, a precoding system using limited feedback with acommon codebook for all pilots of F={F₁, . . . , F₂ _(B) } may send Bbits for each pilot subcarrier for a total feedback load of BK_(pilot)bits per channel block. Given this information, the precoders fornon-pilots may be determined.

It may be possible to weight and sum together the feedback beamformingvectors from the two nearest pilots. The weights may be configured tomaximize the receive SNR of the subcarrier halfway between the twopilots. A transform domain quantization approach may be implemented. Theprecoder interpolation problem may be formulated as a weighted leastsquares problem. The weights may correspond to the distance (in numberof subcarriers) from different pilot precoders. The technique may begeneralized to larger rank precoding interpolation techniques. Ageodesic approach (i.e., linear interpolation on the Grassmann manifold)may also be used. Other interpolation ideas may also be available.Instead of trying to interpolate, another implementation may be basedon, where a common precoder is chosen for several contiguoussubcarriers. The clustering implementation may yield an antenna subsetselection criterion when the cluster is extended to cover all or mostsubcarriers (i.e., only one pilot) and the precoding codebook has the

$\quad\begin{pmatrix}M_{t} \\M\end{pmatrix}$

antenna subset matrices.

The transmitter may recreate precoders employing precoder feedback senton a subset of the subcarriers in conjunction with the channelcorrelation in the frequency domain. Clustering may also be implemented.In this case, the transmitter and receiver may divide (or cluster) thesubcarriers in a predetermined way. All narrowband channels within thecluster may use the same feedback and use the same precoding matrix. Thereceiver may then design the feedback to choose a precoder that ismutually beneficial (e.g., with respect to sum rate).

Alternative techniques besides clustering and interpolation may also beimplemented. For example, Trellis techniques for precoder interpolationmay be used. Successive beamforming taking into account correlation intime and frequency may be implemented. A reduced CSI feedback approachfor MIMO-OFDM may take into account that highly correlated channels mayhave highly correlated feedback values; thus, the number of bits may beeffectively reduced by taking the actual correlation between binarysequences into account.

The multi-mode precoding implementations may also be quantized. In thisscenario, both the matrix and the rank of the matrix may evolve over theOFDM symbol subcarriers. An interpolation framework for multi-modeprecoding may be used.

3GPP LTE and LTE-advanced may employ a MIMO-OFDMA physical layer on thedownlink and may support various single and multiple user MIMO modes ofoperation. Several different single-user codebook based limited feedbacktechniques may be used. Codebook based precoding on the downlink may beimplemented, for example, with two, four, or eight transmit antennas. Inthe case of two antennas, a beamforming codebook with six vectors(including two corresponding to antenna selection) and a precodingcodebook with three matrices may be implemented. For four antennas, afour bit codebook may be used for beamforming and precoding with two,three, and four streams. The precoding codebooks may be built by takingspecific subsets of Householder reflection matrices generated from thebeamforming entries. The subsets may be chosen to have a nestedstructure. For example, for a given generating vector, the two streamcodebook may include the original vector and an additional vector. Thethree stream codebook may add an additional vector and so on. This mayfacilitate multi-mode rank adaptation where the base station may changethe number of active streams, and may offer some computational savings.

3GPP codebooks may use a finite alphabet structure, which may make themeasy to store and may simplify computation.

A second base station may transmit to a first base station a loadindication message. The load indication message may be transmittedperiodically or regularly as needed. The first base station may requesta load indication message and indicate the transmission period andduration. The load indication message may comprise at least one of thefollowing fields: an uplink interference overload, an uplink highinterference indication, a transmit power parameter, and an almost blanksubframe. The transmitter of a load indication message may request asimilar or different load indication message from the base stationreceiving the message. The invoke indication in the message may indicatewhich type of information a base station requesting the other basestation may send back. A base station MAC and physical layer mayschedule and transmit downlink packets based, at least in part, on thereceived load indication messages.

An uplink interference overload for the uplink carrier may indicate thestatus of uplink interference. The uplink carrier may comprise aplurality of uplink resource blocks. The uplink interference overloadmay indicate a status of uplink interference for each uplink resourceblock in the plurality of uplink resource blocks. The status of uplinkinterference may be represented as one of a plurality of predefinedinterference level indicators. The uplink high interference indicationmay comprise a list of a target carrier identifier and a status ofuplink target interference. The status of uplink target interference mayindicate the status of uplink target interference for each resourceblock in the plurality of uplink resource blocks. The status of uplinktarget interference may indicate a high interference sensitivity and/orlow interference sensitivity.

The transmit power parameter for the downlink carrier may comprise astatus of transmit power for each downlink resource block, the number ofantenna ports for the downlink carrier, PDCCH information, beamforminginformation, a combination thereof, and/or the like. The status oftransmit power for downlink resource block(s) may indicate a status oftransmit power for downlink resource block(s) in the plurality ofdownlink resource blocks. The status of transmit power for a downlinkresource block may be one of a first value when transmit power of thedownlink resource block is below a pre-defined threshold and a secondvalue when transmit power of the downlink resource block is below orabove the pre-defined threshold. The PDCCH interference impact may bepresented by predicted number of occupied PDCCH OFDM Symbols. The PDCCHinterference impact may be one of 0, 1, 2, 3, and 4, wherein value 0indicates no prediction is available for load information transmission;

FIG. 12 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention.According to some of the various aspects of embodiments, a first basestation may receive from a second base station at least one applicationprotocol message as shown in 1201. The at least one application protocolmessage may be received, for example from an X2 interface or an S1interface. The first base station and the second base station may beconfigured to communicate with a plurality of wireless devices employinga downlink carrier. The downlink carrier may comprise a plurality ofresource blocks. The at least one application protocol message maycomprise a downlink beamforming information element for at least oneresource block in the downlink carrier. In another implementation atleast one application protocol message may comprise a plurality ofdownlink or uplink beamforming information elements, each one for one ormore resource blocks.

The downlink beamforming information element may indicate a secondbeamforming codeword employed by the second base station for the atleast one resource block. In another example implementation the downlinkbeamforming information element may indicate a plurality of secondbeamforming codeword employed by the second base station for the atleast one resource block. The codewords are employed for beamforming. Inan example implementation, the second beamforming codeword may have anumber of rows or columns equal to a number of antenna ports employed bythe second base station for beamforming on the downlink carrier. Asdescribed previously, an array/matrix may be stored using multipleprogramming code structures. The number of rows or columns refers to theinformation in a codeword which can be stored using various methods. Inanother example embodiment second beamforming codeword may have a numberof rows or columns less than a number of antenna ports employed by thesecond base station for beamforming on the downlink carrier

The second beamforming codeword may be included in (be a part of) asecond beamforming codebook. In an example implementation, the secondbeamforming codeword may be referenced by an index. Instead oftransmitting an entire codeword, the index for the codeword may betransmitted. Correspondence between the beamforming codeword and theindex may be defined by an application protocol message. The applicationprotocol message may be received prior to the at least one applicationprotocol message reception.

The first base station may select for the at least one resource block, afirst beamforming codeword from a first beamforming codebook as shown in1202. The selection may be based, at least in part, on the downlinkbeamforming information element received from the second base station.The first base station may transmit, employing the first beamformingcodeword, signals on a subset of the at least one resource block to awireless device as shown in 1203. The signals may carry control or datapackets for one or more wireless devices.

According to some of the various aspects of embodiments, a first basestation may receive from a second base station at least one applicationprotocol message. The first base station and the second base station maybe configured to communicate with a plurality of wireless devicesemploying a downlink carrier. The downlink carrier may comprise aplurality of resource blocks. The at least one application protocolmessage may comprise a downlink beamforming information element for atleast one resource block in the downlink carrier. The downlinkbeamforming information element may indicate a second beamformingcodeword employed by the second base station for the at least oneresource block. The second beamforming codeword may be referenced by anindex. The second beamforming codeword may be included in a secondbeamforming codebook.

The first base station may select for the at least one resource block, afirst beamforming codeword from a first beamforming codebook. Theselection may be based, at least in part, on the downlink beamforminginformation element received from the second base station. The firstbase station may transmit, employing the first beamforming codeword,signals on a subset of the at least one resource block to a wirelessdevice. The signals may carry control or data packets for one or morewireless devices.

The at least one application protocol message may be transmittedperiodically. At least one application protocol message may furthercomprise a load indication message. At least one application protocolmay comprise a transmit power parameter for the downlink carrier. Thetransmit power parameter may comprise a status of transmit power foreach downlink resource block in the plurality of downlink resourceblocks. The status of transmit power for a downlink resource block maybe one of a first value when transmit power of the downlink resourceblock is below a pre-defined threshold and a second value when transmitpower of the downlink resource block is below or above the pre-definedthreshold.

The subset of the plurality of downlink resource blocks may be selectedbased, at least in part, on the transmit power parameter and thedownlink beamforming information. The first beamforming codebook andsecond beamforming codebook may be the same. The first plurality ofbeamforming codewords may be selected to reduce inter-cell interferencefrom the second base station. The first base station may use informationreceived from at least one wireless device to compute the inter-cellinterference from the second base station. The first base station mayuse a zero-forcing criterion to select a subset of the first pluralityof beamforming codewords. The first base station may use a minimum meansquared error criterion to select a subset of the first plurality ofbeamforming codewords. The first plurality of beamforming codewords maybe selected to reduce inter-cell interference to the second basestation.

The first base station may use information received from at least onewireless device to compute the inter-cell interference to the secondbase station. The first base station may use a maximum signal to leakageratio criterion to select a subset of the plurality of beamformingcodewords. One skilled in the art may use other criterions. The firstbeamforming codebook or the second beamforming codebook may be definedfor a maximum number of transmit antennas and may comprise a set oforiginal codewords. Each original codeword may have a number rows equalto the maximum number of transmit antennas. Codewords for a smallernumber of transmit antennas may be constructed by using a subset of rowsof the original codewords. The first beamforming codebook or the secondbeamforming codebook may be defined for a maximum number of layers andmay comprise a set of original codewords. Each original codeword mayhave a number columns (or rows) equal to the maximum number of layers.Codewords for a smaller number of layers may be constructed by using asubset of columns (or rows) of the original codewords. The first basestation may receive similar application protocol messages from aplurality of second base stations.

The first plurality of beamforming codewords may be selected to reduceinter-cell interference from a subset of the plurality of second basestations. The first base station may use information received from atleast one wireless device to compute the inter-cell interference fromthe subset of the plurality of second base stations. The first basestation may use a zero-forcing criterion to select a subset of the firstplurality of beamforming codewords. The first base station may use aminimum mean squared error criterion to select a subset of the firstplurality of beamforming codewords. The first plurality of beamformingcodewords may be selected to reduce inter-cell interference to a subsetof the plurality of second base stations. The first base station may useinformation received from at least one wireless device to compute theinter-cell interference to the subset of the plurality of second basestations. The first base station may use a maximum signal to leakagecriterion to select a subset of the first plurality of beamformingcodewords. The second base station may transmit the same secondapplication protocol message to a plurality of first base stations. Theplurality of first base stations may select their respective firstplurality of beamforming codewords based on information received fromthe second base station in the second application protocol message.

FIG. 8 is a block diagram for beamforming information exchange accordingto at least one embodiment. In an example embodiment, a first basestation 802 may comprise a communication interface, a processor, and amemory storing instructions that, when executed, cause the first basestation to cause certain functions. The first base station 802 mayreceive at least one application protocol message from a second basestation 801 using interface 807. The second base station 801 maycomprise a downlink carrier comprising a plurality of downlink resourceblocks. The at least one application protocol message may comprisedownlink beamforming information for the downlink carrier. The downlinkbeamforming information may indicate, for each downlink resource blockin the plurality of downlink resource blocks, a beamforming codewordemployed for the downlink resource block. The first base station 802 mayobtain channel state input information for a wireless device based on,at least in part, processing the downlink beamforming information. Thefirst base station may transmit the channel state input information 804to the wireless device 803 in a message, for example, a measurementinformation message. The wireless device 803 may use the channel stateinput information to compute a precoding matrix indicator. The firstbase station 802 may receive a channel state feedback 805 from thewireless device. The channel state feedback may comprise the precodingmatrix indicator. Each of the beamforming codewords may be representedby an index and may belong to a first beamforming codebook. Thecorrespondence between a beamforming codeword and an index may bedefined by an application protocol message received prior to the atleast one application protocol message reception. The base station maytransmit packets to the wireless device 803 using beamformingtransmission 806.

FIG. 9 depicts message flow between a base station 902 and a wirelessdevice 901, according to at least one embodiment. The first base station902 may receive at least one application protocol message from a secondbase station in the plurality of base stations. The second base stationmay comprise a downlink carrier comprising a plurality of downlinkresource blocks. The at least one application protocol message maycomprise the number of antenna ports for the downlink carrier anddownlink beamforming information for the downlink carrier. The downlinkbeamforming information may indicate, for each downlink resource blockin the plurality of downlink resource blocks, a beamforming codewordemployed for the downlink resource block. Each of the beamformingcodewords may depend on the number of antenna ports and may berepresented by an index and belonging to a first beamforming codebook.The first base station may select a subset of the downlink beamforminginformation for wireless device 901. The first base station 902 maytransmit a control message 903 to wireless device 901. The controlmessage may comprise an identifier of the second base station, and thesubset of the downlink beamforming information. First base station 902may receive a channel state feedback 904 from the wireless device 901.The channel state feedback may comprise a precoding matrix indicator.The wireless device 901 may measure reference signals received from thesecond base station and process the measured reference signals based, atleast in part, on the subset to compute the precoding matrix indicator.The first base station 902 may transmit packets to the wireless device901 using beamforming transmission 905.

FIG. 13 depicts an example flow chart for a base station employingbeamforming as per an aspect of an embodiment of the present invention.A first base station may receive from a second base station at least oneapplication protocol message as shown in 1301. The first base stationand the second base station may be configured to communicate with aplurality of wireless devices employing a downlink carrier. The downlinkcarrier may comprise a plurality of resource blocks. The at least oneapplication protocol message may comprise a downlink beamforminginformation element for at least one resource block in the downlinkcarrier. The downlink beamforming information element may indicate asecond beamforming codeword employed by the second base station for theat least one resource block. The second beamforming codeword may beincluded in (be a part of) a second beamforming codebook. The first basestation may compute a channel state input information element for awireless device based on, at least in part, processing the downlinkbeamforming information element as shown in 1302. The first base stationmay transmit the channel state input information element to the wirelessdevice for computing a precoding matrix indicator as shown in 1303. Thefirst base station may receive a channel state feedback from thewireless device. The channel state feedback may comprise the precodingmatrix indicator as shown in 1304.

According to some of the various aspects of embodiments, a wirelessdevice may receive channel state input information from a first basestation. The wireless device may compute a precoding matrix indicatorusing the channel state input information. The wireless device maytransmit a channel state information comprising the precoding matrixindicator to the first base station.

According to some of the various aspects of embodiments, the wirelessdevice may receive channel state input information from a first basestation in the plurality of base stations. The first base station mayobtain the channel state input information based, at least in part, onprocessing downlink beamforming information received from a second basestation in the plurality of base stations. The first base station maycompute a precoding matrix indicator using the channel state inputinformation. The first base station may transmit a channel stateinformation comprising the precoding matrix indicator to the first basestation.

According to some of the various aspects of embodiments, the wirelessdevice may receive channel state input information from a first basestation in the plurality of base stations. The first base station mayobtain the channel state input information based, at least in part, onprocessing downlink beamforming information received from a second basestation in the plurality of base stations. The second base station maycomprise a downlink carrier comprising a plurality of downlink resourceblocks. The downlink beamforming information may indicate a beamformingcodeword employed by the second base station for each downlink resourceblock in the plurality of downlink resource blocks. The wireless devicemay compute a precoding matrix indicator using the channel state inputinformation. The wireless device may transmit channel state informationcomprising the precoding matrix indicator to the first base station.

According to some of the various aspects of embodiments, the wirelessdevice may receive a control message from a first base station in theplurality of base stations. The control message may comprise anidentifier of a second base station in the plurality of base stations,and channel state input information. The channel state input informationmay be a subset of downlink beamforming information received from thesecond base station. The second base station may comprise a downlinkcarrier comprising a plurality of downlink resource blocks. The downlinkbeamforming information may indicate a beamforming codeword employed bythe second base station for each downlink resource block in theplurality of downlink resource blocks. The wireless device may measurereference signals received from the second base station. The wirelessdevice may process the measured reference signals based, at least inpart, on the channel state input information to compute a precodingmatrix indicator. The wireless device may transmit channel stateinformation comprising the precoding matrix indicator to the first basestation. The processing of the measured reference signals may comprisemultiplying measured reference signal(s) by at least one codeword in thechannel state input information.

According to some of the various aspects of embodiments, a wirelessdevice may receive a control message from a first base station. Thecontrol message may comprise an identifier of a second base station inthe plurality of base stations. The control message may comprise achannel state input information element. The channel state inputinformation element may be based, at least in part, on a downlinkbeamforming information element received by the first base station froma second base station. The downlink beamforming information element mayindicate a beamforming codeword employed by the second base station forat least one downlink resource block. The wireless device may measurereference signals received from the second base station. The wirelessdevice may process the measured reference signals based, at least inpart, on the channel state input information element to compute aprecoding matrix indicator. The wireless device may transmit a channelstate information comprising the precoding matrix indicator to the firstbase station. The processing of the measured reference signals maycomprise multiplying measured reference signal by at least one codewordin the channel state input information.

According to some of the various aspects of embodiments, a wirelessdevice may receive from a first base station a channel state inputinformation element. The channel state input information element may bebased, at least in part, on a downlink beamforming information elementreceived by the first base station from a second base station. Thedownlink beamforming information element may indicate a beamformingcodeword employed by the second base station for at least one downlinkresource block. The wireless device may compute a precoding matrixindicator employing the channel state input information element. Thewireless device may transmit channel state information comprising theprecoding matrix indicator to the first base station.

The channel state input information may be a codebook subset restrictionbitmap parameter. The wireless device may select a precoding matrixindicator from a subset of the precoding codebook indicated by thecodebook subset restriction bitmap parameter. The processing of themeasured reference signals may include vector quantization and encoding.The processing of the measured reference signals may comprisemultiplying measured reference signal(s) by at least one codeword in thedownlink beamforming information. The wireless device may furthermeasure the data signals received from the base station. The precodingmatrix indicator may be calculated to reduce downlink inter-cellinterference. The channel state feedback may further comprise a channelquality indicator. The channel state feedback may further comprise arank indicator. The precoding matrix indicator may be selected from aplurality of predetermined precoding matrix indicators.

The first base station may transmit a plurality of packets to thewireless device. The plurality of packets may be transmitted using theprecoding matrix indicator. The precoding matrix indicator may becomputed for a sub-band of the downlink carrier. The first base stationmay further transmit at least one control message to the wirelessdevice. The at least one control message may configure measurementparameters of the wireless device. The first base station maydemodulate, despread, and decode the received channel state feedback.The channel state feedback may be modulated using SC-FDMA. The subset ofthe downlink beamforming information may comprise a plurality ofbeamforming codewords employed for a subset of the plurality of downlinkresource blocks. The wireless device may use a zero-forcing criterion tocompute the precoding matrix indicator. The wireless device may use aminimum mean squared error criterion to compute the precoding matrixindicator.

The subset of downlink beamforming information may comprise beaminformation from the second base station that causes substantialinter-cell interference to the wireless device. The first beamformingcodebook may be defined for a maximum number of transmit antennas andmay comprise a set of original codewords. Each original codeword mayhave a number of rows (or columns) equal to the maximum number oftransmit antennas. Codewords for a smaller number of transmit antennasmay be constructed by using a subset of rows (or columns) of theoriginal codewords. The first beamforming codebook may be defined for amaximum number of layers and comprise a set of original codewords. Eachoriginal codeword may have a number of columns (or rows) equal to themaximum number of layers. Codewords for a smaller number of layers maybe constructed by using a subset of columns of the original codewords.The smaller number of layers may be equal to a rank indicated by thewireless device through a rank indicators field in the channel statefeedback.

Embodiments of the present invention enable the intelligent transfer ofa wireless device between base stations that accounts for configurationof channel state information reference signals and configuration ofchannel state information interference measurement resources. An issuewith respect to configuration of channel state information referencesignals and configuration of channel state information interferencemeasurement resources is the maintenance and updating of carrierconfigurations during a wireless device handover from a serving basestation to a target base station. A wireless device may be configuredwith configuration of channel state information reference signals andconfiguration of channel state information interference measurementresources with a serving base station. A target base station maymaintain the same configuration, or may direct the updating of awireless device's configuration. There is a need for developing asignalling flow, wireless device processes, and base station processesto address wireless device configuration of channel state informationreference signals and configuration of channel state informationinterference measurement resources during a handover to reduce handoveroverhead and handover delay.

According to some of the various aspects of embodiments, in connectedmode, the network may control wireless device mobility. For example, thenetwork may decide when and to which base station the wireless deviceconnects. For network controlled mobility in connected mode, a primarycarrier may be changed using an RRC connection reconfiguration messagethat includes mobility control information (handover). The network maytrigger the handover procedure (e.g. based on radio conditions, load,QoS, wireless device category, and/or the like). The network mayconfigure the wireless device to perform measurement reporting. Thenetwork may also initiate a handover blindly (e.g. without havingreceived measurement reports from the wireless device). Before sendingthe handover message to the wireless device, the source base station mayprepare one or more target cells. The source base station may select atarget primary cell. The source base station may also provide the targetbase station with a list of best cells on a frequency for whichmeasurement information is available (e.g. in order of decreasing signalstrength level). The source base station may also include availablemeasurement information for the cells provided in the list. The targetbase station may decide configuration of channel state informationreference signals and configuration of channel state informationinterference measurement resources after the handover, which may includeconfiguration parameters other than the ones indicated by the sourcebase station.

The target base station may generate a message used to configure channelstate information reference signals and channel state informationinterference measurement resources for the wireless device for thehandover, for example, the message including carrier configurationparameters to be used in the target base station. The source basestation may transparently (e.g., may not alter values/content) forwardthe handover message/information received from the target base stationto the wireless device. After receiving the handover message, thewireless device may attempt to access the target primary cell at theavailable random access channel resources according to a random accessresource selection. Upon successful completion of the handover, thewireless device may send a message used to confirm the handover to thetarget base station. The wireless device may use the target carrierconfiguration received from the source base station in communicatingwith the target base station.

According to some of the various aspects of embodiments, a base stationmay receive a first message indicating wireless device capability. Thebase station may consider a wireless device's capability in configuringchannel state information reference signals and channel stateinformation interference measurement resources for a wireless device. Awireless device may be configured with a configuration that iscompatible with the wireless device's capability. Configurationcapability for processing multiple channel state information referencesignals and processing multiple channel state information interferencemeasurement resources may not be supported by wireless devices notcompatible with LTE release 11 or above. A wireless device may transmitits capability to a base station via an RRC message. The base stationmay consider wireless device capability in configuring multiple channelstate information reference signals and multiple channel stateinformation interference measurement resources for the wireless device.

The wireless device context within the source base station may containinformation regarding roaming/handover restrictions which may beprovided either at connection establishment or at the last tracking areaupdate process. The source base station may configure the wirelessdevice measurement procedures employing at least one RRC connectionreconfiguration message. The wireless device may be triggered to send atleast one measurement report by the rules set by, for example: systeminformation, RRC configuration, and/or the like. The source base stationmay make a handover decision based on many parameters, such as:measurement reports, radio resource configuration information, trafficand load information, a combination of the above, and/or the like. Thesource base station may initiate the handover procedure by sending ahandover request message to one or more potential target base stations.

The source base station may transmit a handover request message to oneor more potential target base stations by passing information to preparethe handover at the target side. The handover request message maycomprise information indicating the wireless device's capabilityregarding support for processing multiple channel state informationreference signals and configuration of multiple channel stateinformation interference measurement resources. The target base stationmay employ the capability of the wireless device in order to properlyconfigure carrier configuration of the wireless device before thewireless device connects to the target base station. The target basestation may configure the wireless device considering the configurationlimitations and capabilities of the wireless device. For example, if thewireless device does not support configuration of multiple channel stateinformation reference signals and/or configuration of multiple channelstate information interference measurement resources, the target basestation may avoid trying to configure the wireless device with thoseconfiguration options. In another example embodiment, handover requestmessages may further comprise the current multiple channel stateinformation reference signals configuration parameters and/or multiplechannel state information interference measurement resourcesconfiguration parameters of the wireless device connected to the servingbase station. During the handover preparation phase, the serving basestation may transmit wireless device's configuration capability and/orwireless device's current configuration to one or more potential targetbase stations. In an example embodiment, the serving base station mayprovide information such as, for example, about wireless devicededicated radio resource configurations. This may, for example, include:multiple channel state information reference signals parameters,multiple channel state information interference measurement resourcesparameters, carrier parameters, enhanced PDCCH parameters, PDSCHparameters, physical layer parameters and channel parameters, powercontrol parameters, carrier configuration parameters, frequencyinformation, carrier type, cross carrier scheduling parameters, and/ordedicated MAC configuration parameters, a combination thereof, and/orthe like. This information may be employed, at least in part, by thepotential target base station to configure the wireless device, forexample, to configure multiple channel state information referencesignals parameters and multiple channel state information interferencemeasurement resources parameters.

According to some of the various aspects of embodiments, handoveradmission control may be performed by the target base station dependenton many factors (e.g. QoS required for the wireless device bearers,wireless device capabilities, wireless device configuration, target basestation load, a combination of the above, and/or the like). The targetbase station may configure the required resources according to thereceived information from the serving base station. The radio accessconfiguration to be used in the target carrier may be specifiedindependently (for example as an establishment) or as a delta comparedto the radio access configuration used in the source cell (for exampleas a reconfiguration).

The target base station may prepare a handover and may send a handoverrequest acknowledge message to a source base station. The handoverrequest acknowledge message may include a transparent container to besent to the wireless device as an RRC message to perform the handover.The container may include a new C-RNTI, target base station securityalgorithm identifiers for the selected security algorithms, a dedicatedRACH preamble, access parameters, SIBs, and/or other configurationparameters. The transparent container may further comprise the multiplechannel state information reference signals configuration parametersand, multiple channel state information interference measurementresources configuration parameters for connection of the wireless deviceto the target base station. The updated configurations may modify theexisting configuration of the wireless device or may keep the samecarrier configuration that the wireless device has with the serving basestation. The target base station may generate the RRC message to performthe handover, for example, the RRC connection reconfiguration messageincluding the mobility control information. The RRC message may be sentby the source base station towards the wireless device. The source basestation may perform the necessary integrity protection and ciphering ofthe message. The wireless device may receive the RRC connectionreconfiguration message from the source base station and may startperforming the handover.

After receiving the RRC connection reconfiguration message, includingthe mobility control information, the wireless device may performsynchronization to the target base station and access the target cellvia a random access channel on a primary cell. The wireless device mayderive target base station specific keys and may configure the selectedsecurity algorithms to be used in the target cell. The target basestation may respond with uplink allocation and timing advanceinformation. After the wireless device has successfully accessed thetarget cell, the wireless device may send an RRC connectionreconfiguration complete message to confirm the handover and to indicatethat the handover procedure is completed for the wireless device. Thetarget base station may now begin sending and receiving data with thewireless device.

FIG. 14 depicts an example flow chart for a handover process as per anaspect of an embodiment of the present invention. According to some ofthe various aspects of embodiments, a serving base station may receive afirst message from a wireless device on a carrier. The first message maycomprise one or more parameters implicitly or explicitly indicatingwhether the wireless device supports configuration of: a) a maximum of kchannel state information reference signals for the carrier, k being aninteger greater than one; and b) a maximum of n channel stateinformation interference measurement resources for the carrier, n beingan integer greater than one. For example, the first message may includea first parameter that indicates whether the wireless device supportsprocessing multiple channel state information reference signals andconfiguration of multiple channel state information interferencemeasurement resources. In another example, the first message may includea parameter indicating the release version of the wireless device, whichmay implicitly indicate whether the wireless device supports multiplechannel state information reference signals and configuration ofmultiple channel state information interference measurement resources.In another example, a parameter may indicate radio capabilities of thewireless device which implicitly or explicitly indicate whether thewireless device supports processing multiple channel state informationreference signals and configuration of multiple channel stateinformation interference measurement resources. In an exampleembodiment, k may be equal to n. In an implementation example, a firstvalue of a capability parameter in the first message may indicate afirst k value and a first n value. A second value of a capabilityparameter may indicate a second k value and a second n value. In anotherexample embodiment, a parameter in the first message may determine adevice category, which in turn may determine a value for k and n. Forexample, a first device category may indicate that k=n=5, and a seconddevice category may indicate k=7, and n=6.

The serving base station may transmit at least one second message to thewireless device. At least some parameters in the at least one secondmessage may depend at least in part on the first message. For example,if the first message indicates that the device supports processingmultiple channel state information reference signals and configurationof multiple channel state information interference measurementresources, at least some parameters in the at least one second messagemay configure these parameters. In another example, if the first messageindicates that the wireless device supports non-backward compatiblecarriers, then the base station may configure non-backward compatiblecarriers for the carrier. The base station may configure the wirelessdevice considering the capability parameters of the wireless devicereceived in the first message. For example, if the first messageindicates certain capability in the wireless device, the base stationmay configure those capabilities. In another example, if the first basestation indicates that certain capabilities are not supported in thewireless device, the base station may not configure those capabilities.For example, if the wireless device does not support multiple timealignment groups, the base station may not configure multiple timealignment groups for the wireless device.

According to some of the various aspects of embodiments, the at leastone second message may comprise: one or more channel state informationreference signals parameters, one or more channel state informationinterference measurement resources parameters, a plurality ofmeasurement parameters, and/or a combination of the above. The at leastone second message may be configured to cause configured to cause: a)configuration of j channel state information reference signals for thecarrier, j being an integer smaller than or equal to k, b) configurationof m channel state information interference measurement resources forthe carrier, m being an integer smaller than or equal to n, c) thewireless device measuring signal quality of at least one carrier of oneor more target base stations in response to the measurement parameters,d) one or more of the above configurations in a, b, and c. The basestation may configure the channel state information reference signalsand channel state information interference measurement resources withinthe capability of the wireless device.

The base station may configure multiple channel state informationreference signals (CSI-RSs). Each of the many CSI-RSs may beperiodically transmitted on downlink OFDM radio resources according toits configuration parameters. CSI-RSs signal codes are known by thewireless device. The wireless device may measure the CSI-RSs and mayreport back CSI-RSs measurement information to the base station. Thebase station may configure a plurality of carriers for a wireless deviceand each carrier may be configured to transmit a plurality of CSI-RSs tothe wireless device. CSI-RSs on different carriers may or may not havethe same configuration. The wireless device may measure CSI-RSs onactivated carriers and may report the measurements back to the basestation. The base station may also configure a plurality of channelstate information interference measurement resources (CSI-IMs). In anexample embodiment, the base station may not transmit information inOFDM radio resources defined by CSI-IMs configuration parameters. Thewireless device may measure interference in OFDM radio resources definedby CSI-IMs configuration parameters and may report this information backto the base station. The base station may configure a plurality ofcarriers for a wireless device and each carrier may be configured with aplurality of CSI-IMs to the wireless device. The wireless device maymeasure interference in CSI-IM resources on activated carriers and mayreport them back to the base station. CSI-IM configuration on differentcarriers may use the same or different configuration parameters.

According to some of the various aspects of embodiments, the servingbase station may receive at least one measurement report from thewireless device. The serving base station may receive at least onemeasurement report from the wireless device in response to the at leastone second message. The at least one measurement report may comprisesignal quality information of at least one carrier the at least onecarrier of at least one of the one or more target base stations. Thesignal quality information may be derived at least in part employingmeasurements of at least one OFDM subcarrier. The base station mayreceive CSI-RS measurement reports and measurement reports of targetbase stations signals. These two category of measurement reports mayhave different formats and may be transmitted separately to the servingbase station at different times employing different uplinkmessages/signals.

The serving base station may make a handover decision based at least inpart on the at least one measurement report. The serving base stationmay transmit in response to the serving base station making a handoverdecision for the wireless device, at least one third message to at leastone target base station. The at least one third message may comprise theone or more parameters implicitly or explicitly indicating whether thewireless device supports the configuration of: a) the maximum of kchannel state information reference signals; and/or b) the maximum of nchannel state information interference measurement resources. The atleast one third message may further comprise configuration parametersof: a) the j channel state information reference signals for thecarrier; and/or b) the m channel state information interferencemeasurement resources for the carrier.

According to some of the various aspects of embodiments, before the atleast one second message is transmitted, the serving base station mayencrypt the at least one second message; and/or may protect the at leastone second message by an integrity header. The at least one secondmessage may further include configuration information for physicalchannels for the wireless device. The at least one second message may beconfigured to cause the wireless device to set up or modify at least oneradio bearer. One of the at least one second message may be configuredto cause the wireless device to configure at least one of a physicallayer parameter, a media access control layer parameter and a radio linkcontrol layer parameter.

One of the at least one second message may comprise radio linkconfiguration information comprising uplink channel configurationparameters and handover parameters. One of the at least one secondmessage may comprise radio resource configuration parameters comprisinga physical channel configuration parameters. The serving base stationmay transmit a demodulation reference signal on the carrier.

According to some of the various aspects of embodiments, a serving basestation may receive a first message from a wireless device on a carrier.The first message may comprise one or more parameters implicitly orexplicitly indicating whether the wireless device supports configurationof a maximum of k channel state information reference signals for thecarrier, k being an integer greater than one. The first message mayfurther comprise one or more parameters implicitly or explicitlyindicating whether the wireless device supports configuration of amaximum of n channel state information interference measurementresources for the carrier, n being an integer greater than one.

The serving base station may transmit to the wireless device, at leastone second message. At least some parameters in the at least one secondmessage may depend at least in part on the first message. The at leastone second message may be configured to cause configuration of j channelstate information reference signals for the carrier, j being an integersmaller than or equal to k. The at least one second message may beconfigured to further cause configuration of m channel state informationinterference measurement resources for the carrier, m being an integersmaller than or equal to n. The serving base station may transmit inresponse to the serving base station making a handover decision for thewireless device, at least one third message to at least one target basestation. The at least one third message may comprising at least one of:a) the one or more parameters, b) configuration parameters of the jchannel state information reference signals and/or the m channel stateinformation interference measurement resources. The one or moreparameters may implicitly or explicitly indicating whether the wirelessdevice supports the configuration of the maximum of k channel stateinformation reference signals; and/or the maximum of n channel stateinformation interference measurement resources.

The disclosed embodiment considers two sets of configuration parameters,one for multiple channel state information reference signals and theother for multiple channel state information interference measurementresources. Some embodiments of the invention may be implementedincluding one of these sets. For example, the disclosed handoverprocesses may consider configuration of multiple channel stateinformation reference signals and not consider configuration of multiplechannel state information interference measurement resources. In anotherexample embodiment, the disclosed handover processes may considerconfiguration of multiple channel state information interferencemeasurement resources and not consider configuration of multiple channelstate information reference signals.

FIG. 15 depicts an example flow chart for a handover process as per anaspect of an embodiment of the present invention. According to some ofthe various aspects of embodiments, a serving base station may transmitin response to the serving base station making a handover decision for awireless device, at least one first message to at least one target basestation. The at least one first message may comprise one or moreparameters implicitly or explicitly indicating whether the wirelessdevice supports configuration of a) a maximum of k channel stateinformation reference signals for a carrier, k being an integer greaterthan one; and/or b) a maximum of n channel state informationinterference measurement resources for the carrier, n being an integergreater than one.

The at least one first message may further comprise configurationparameters of: a) j channel state information reference signals for thecarrier, j being an integer smaller than or equal to k; and/or m channelstate information interference measurement resources for the carrier, mbeing an integer smaller than or equal to n. The at least one firstmessage may comprise one of many of the above parameters. In differentexample embodiments of the invention, the at least one first message maycomprise at least one of, or all of, or some of the above parameters.

The serving base station may receive at least one second message fromone of the at least one target base station. The at least one secondmessage may comprise configuration parameters of: p channel stateinformation reference signals for the carrier, p being an integersmaller than or equal to k; and/or q channel state informationinterference measurement resources for the carrier, q being an integersmaller than or equal to n. The configuration parameters in the at leastone second message are within the capability of the wireless device asindicated in the at least one first message.

The serving base station may transmit in response to receiving the atleast one second message, a third message to the wireless device. Thethird message may comprise the configuration parameters of: the pchannel state information reference signals; and/or the q channel stateinformation interference measurement resources. The serving base stationtransmits this configuration along with a handover command in an RRCmessage to the wireless device. The wireless device then synchronizeswith the target base station and connects to the target base stationaccording to the configuration parameters received in the third message.

According to some of the various aspects of embodiments, before thethird message is transmitted, the serving base station may encrypt thethird message; and may protect the third message by an integrity header.The third message may further include configuration information forphysical channels for the wireless device. The third message may beconfigured to cause the wireless device to set up or modify at least oneradio bearer. The third message may be configured to cause the wirelessdevice to configure at least one of a physical layer parameter, a mediaaccess control layer parameter and an radio link control layerparameter. The third message may comprise radio link configurationinformation comprising uplink channel configuration parameters andhandover parameters.

According to some of the various aspects of embodiments, the thirdmessage may comprise at least one radio resource configuration parametercomprising at least one physical channel configuration parameter. Theone of the at least one target base station may transmit a plurality ofchannel state information reference signals on the carrier. The one ofthe at least one target base station may transmit a plurality of ademodulation reference signals on the carrier. The third message mayfurther comprise configuration parameters of a plurality of carriers.

According to some of the various aspects of embodiments, the packets inthe downlink may be transmitted via downlink physical channels. Thecarrying packets in the uplink may be transmitted via uplink physicalchannels. The baseband data representing a downlink physical channel maybe defined in terms of at least one of the following actions: scramblingof coded bits in codewords to be transmitted on a physical channel;modulation of scrambled bits to generate complex-valued modulationsymbols; mapping of the complex-valued modulation symbols onto one orseveral transmission layers; precoding of the complex-valued modulationsymbols on layer(s) for transmission on the antenna port(s); mapping ofcomplex-valued modulation symbols for antenna port(s) to resourceelements; and/or generation of complex-valued time-domain OFDM signal(s)for antenna port(s).

Codeword, transmitted on the physical channel in one subframe, may bescrambled prior to modulation, resulting in a block of scrambled bits.The scrambling sequence generator may be initialized at the start ofsubframe(s). Codeword(s) may be modulated using QPSK, 16QAM, 64QAM,128QAM, and/or the like resulting in a block of complex-valuedmodulation symbols. The complex-valued modulation symbols for codewordsto be transmitted may be mapped onto one or several layers. Fortransmission on a single antenna port, a single layer may be used. Forspatial multiplexing, the number of layers may be less than or equal tothe number of antenna port(s) used for transmission of the physicalchannel. The case of a single codeword mapped to multiple layers may beapplicable when the number of cell-specific reference signals is four orwhen the number of UE-specific reference signals is two or larger. Fortransmit diversity, there may be one codeword and the number of layersmay be equal to the number of antenna port(s) used for transmission ofthe physical channel.

The precoder may receive a block of vectors from the layer mapping andgenerate a block of vectors to be mapped onto resources on the antennaport(s). Precoding for spatial multiplexing using antenna port(s) withcell-specific reference signals may be used in combination with layermapping for spatial multiplexing. Spatial multiplexing may support twoor four antenna ports and the set of antenna ports used may be {0,1} or{0, 1, 2, 3}. Precoding for transmit diversity may be used incombination with layer mapping for transmit diversity. The precodingoperation for transmit diversity may be defined for two and four antennaports. Precoding for spatial multiplexing using antenna ports withUE-specific reference signals may also, for example, be used incombination with layer mapping for spatial multiplexing. Spatialmultiplexing using antenna ports with UE-specific reference signals maysupport up to eight antenna ports. Reference signals may be pre-definedsignals that may be used by the receiver for decoding the receivedphysical signal, estimating the channel state, and/or other purposes.

For antenna port(s) used for transmission of the physical channel, theblock of complex-valued symbols may be mapped in sequence to resourceelements. In resource blocks in which UE-specific reference signals arenot transmitted the PDSCH may be transmitted on the same set of antennaports as the physical broadcast channel in the downlink (PBCH). Inresource blocks in which UE-specific reference signals are transmitted,the PDSCH may be transmitted, for example, on antenna port(s) {5, {7},{8}, or {7, 8, . . . , v+6}, where v is the number of layers used fortransmission of the PDSCH.

Common reference signal(s) may be transmitted in physical antennaport(s). Common reference signal(s) may be cell-specific referencesignal(s) (RS) used for demodulation and/or measurement purposes.Channel estimation accuracy using common reference signal(s) may bereasonable for demodulation (high RS density). Common referencesignal(s) may be defined for LTE technologies, LTE-advancedtechnologies, and/or the like. Demodulation reference signal(s) may betransmitted in virtual antenna port(s) (i.e., layer or stream). Channelestimation accuracy using demodulation reference signal(s) may bereasonable within allocated time/frequency resources. Demodulationreference signal(s) may be defined for LTE-advanced technology and maynot be applicable to LTE technology. Measurement reference signal(s),may also called CSI (channel state information) reference signal(s), maybe transmitted in physical antenna port(s) or virtualized antennaport(s). Measurement reference signal(s) may be Cell-specific RS usedfor measurement purposes. Channel estimation accuracy may be relativelylower than demodulation RS. CSI reference signal(s) may be defined forLTE-advanced technology and may not be applicable to LTE technology.

In at least one of the various embodiments, uplink physical channel(s)may correspond to a set of resource elements carrying informationoriginating from higher layers. The following example uplink physicalchannel(s) may be defined for uplink: a) Physical Uplink Shared Channel(PUSCH), b) Physical Uplink Control Channel (PUCCH), c) Physical RandomAccess Channel (PRACH), and/or the like. Uplink physical signal(s) maybe used by the physical layer and may not carry information originatingfrom higher layers. For example, reference signal(s) may be consideredas uplink physical signal(s). Transmitted signal(s) in slot(s) may bedescribed by one or several resource grids including, for example,subcarriers and SC-FDMA or OFDMA symbols. Antenna port(s) may be definedsuch that the channel over which symbol(s) on antenna port(s) may beconveyed and/or inferred from the channel over which other symbol(s) onthe same antenna port(s) is/are conveyed. There may be one resource gridper antenna port. The antenna port(s) used for transmission of physicalchannel(s) or signal(s) may depend on the number of antenna port(s)configured for the physical channel(s) or signal(s).

Element(s) in a resource grid may be called a resource element. Aphysical resource block may be defined as N consecutive SC-FDMA symbolsin the time domain and/or M consecutive subcarriers in the frequencydomain, wherein M and N may be pre-defined integer values. Physicalresource block(s) in uplink(s) may comprise of M×N resource elements.For example, a physical resource block may correspond to one slot in thetime domain and 180 kHz in the frequency domain. Baseband signal(s)representing the physical uplink shared channel may be defined in termsof: a) scrambling, b) modulation of scrambled bits to generatecomplex-valued symbols, c) mapping of complex-valued modulation symbolsonto one or several transmission layers, d) transform precoding togenerate complex-valued symbols, e) precoding of complex-valued symbols,f) mapping of precoded complex-valued symbols to resource elements, g)generation of complex-valued time-domain SC-FDMA signal(s) for antennaport(s), and/or the like.

For codeword(s), block(s) of bits may be scrambled with UE-specificscrambling sequence(s) prior to modulation, resulting in block(s) ofscrambled bits. Complex-valued modulation symbols for codeword(s) to betransmitted may be mapped onto one, two, or more layers. For spatialmultiplexing, layer mapping(s) may be performed according to pre-definedformula (s). The number of layers may be less than or equal to thenumber of antenna port(s) used for transmission of physical uplinkshared channel(s). The example of a single codeword mapped to multiplelayers may be applicable when the number of antenna port(s) used forPUSCH is, for example, four. For layer(s), the block of complex-valuedsymbols may be divided into multiple sets, each corresponding to oneSC-FDMA symbol. Transform precoding may be applied. For antenna port(s)used for transmission of the PUSCH in a subframe, block(s) ofcomplex-valued symbols may be multiplied with an amplitude scalingfactor in order to conform to a required transmit power, and mapped insequence to physical resource block(s) on antenna port(s) and assignedfor transmission of PUSCH.

According to some of the various embodiments, data may arrive to thecoding unit in the form of two transport blocks every transmission timeinterval (TTI) per UL cell. The following coding actions may beidentified for transport block(s) of an uplink carrier: a) Add CRC tothe transport block, b) Code block segmentation and code block CRCattachment, c) Channel coding of data and control information, d) Ratematching, e) Code block concatenation. f) Multiplexing of data andcontrol information, g) Channel interleaver, h) Error detection may beprovided on UL-SCH (uplink shared channel) transport block(s) through aCyclic Redundancy Check (CRC), and/or the like. Transport block(s) maybe used to calculate CRC parity bits. Code block(s) may be delivered tochannel coding block(s). Code block(s) may be individually turboencoded. Turbo coded block(s) may be delivered to rate matchingblock(s).

Physical uplink control channel(s) (PUCCH) may carry uplink controlinformation. Simultaneous transmission of PUCCH and PUSCH from the sameUE may be supported if enabled by higher layers. For a type 2 framestructure, the PUCCH may not be transmitted in the UpPTS field. PUCCHmay use one resource block in each of the two slots in a subframe.Resources allocated to UE and PUCCH configuration(s) may be transmittedvia control messages. PUCCH may comprise: a) positive and negativeacknowledgements for data packets transmitted at least one downlinkcarrier, b) channel state information for at least one downlink carrier,c) scheduling request, and/or the like.

According to some of the various aspects of embodiments, cell search maybe the procedure by which a wireless device may acquire time andfrequency synchronization with a cell and may detect the physical layerCell ID of that cell (transmitter). An example embodiment forsynchronization signal and cell search is presented below. A cell searchmay support a scalable overall transmission bandwidth corresponding to 6resource blocks and upwards. Primary and secondary synchronizationsignals may be transmitted in the downlink and may facilitate cellsearch. For example, 504 unique physical-layer cell identities may bedefined using synchronization signals. The physical-layer cellidentities may be grouped into 168 unique physical-layer cell-identitygroups, group(s) containing three unique identities. The grouping may besuch that physical-layer cell identit(ies) is part of a physical-layercell-identity group. A physical-layer cell identity may be defined by anumber in the range of 0 to 167, representing the physical-layercell-identity group, and a number in the range of 0 to 2, representingthe physical-layer identity within the physical-layer cell-identitygroup. The synchronization signal may include a primary synchronizationsignal and a secondary synchronization signal.

According to some of the various aspects of embodiments, the sequenceused for a primary synchronization signal may be generated from afrequency-domain Zadoff-Chu sequence according to a pre-defined formula.A Zadoff-Chu root sequence index may also be predefined in aspecification. The mapping of the sequence to resource elements maydepend on a frame structure. The wireless device may not assume that theprimary synchronization signal is transmitted on the same antenna portas any of the downlink reference signals. The wireless device may notassume that any transmission instance of the primary synchronizationsignal is transmitted on the same antenna port, or ports, used for anyother transmission instance of the primary synchronization signal. Thesequence may be mapped to the resource elements according to apredefined formula.

For FDD frame structure, a primary synchronization signal may be mappedto the last OFDM symbol in slots 0 and 10. For TDD frame structure, theprimary synchronization signal may be mapped to the third OFDM symbol insubframes 1 and 6. Some of the resource elements allocated to primary orsecondary synchronization signals may be reserved and not used fortransmission of the primary synchronization signal.

According to some of the various aspects of embodiments, the sequenceused for a secondary synchronization signal may be an interleavedconcatenation of two length-31 binary sequences. The concatenatedsequence may be scrambled with a scrambling sequence given by a primarysynchronization signal. The combination of two length-31 sequencesdefining the secondary synchronization signal may differ betweensubframe 0 and subframe 5 according to predefined formula (s). Themapping of the sequence to resource elements may depend on the framestructure. In a subframe for FDD frame structure and in a half-frame forTDD frame structure, the same antenna port as for the primarysynchronization signal may be used for the secondary synchronizationsignal. The sequence may be mapped to resource elements according to apredefined formula.

Example embodiments for the physical channels configuration will now bepresented. Other examples may also be possible. A physical broadcastchannel may be scrambled with a cell-specific sequence prior tomodulation, resulting in a block of scrambled bits. PBCH may bemodulated using QPSK, and/or the like. The block of complex-valuedsymbols for antenna port(s) may be transmitted during consecutive radioframes, for example, four consecutive radio frames. In some embodimentsthe PBCH data may arrive to the coding unit in the form of a onetransport block every transmission time interval (TTI) of 40 ms. Thefollowing coding actions may be identified. Add CRC to the transportblock, channel coding, and rate matching. Error detection may beprovided on PBCH transport blocks through a Cyclic Redundancy Check(CRC). The transport block may be used to calculate the CRC parity bits.The parity bits may be computed and attached to the BCH (broadcastchannel) transport block. After the attachment, the CRC bits may bescrambled according to the transmitter transmit antenna configuration.Information bits may be delivered to the channel coding block and theymay be tail biting convolutionally encoded. A tail bitingconvolutionally coded block may be delivered to the rate matching block.The coded block may be rate matched before transmission.

A master information block may be transmitted in PBCH and may includesystem information transmitted on broadcast channel(s). The masterinformation block may include downlink bandwidth, system framenumber(s), and PHICH (physical hybrid-ARQ indicator channel)configuration. Downlink bandwidth may be the transmission bandwidthconfiguration, in terms of resource blocks in a downlink, for example 6may correspond to 6 resource blocks, 15 may correspond to 15 resourceblocks and so on. System frame number(s) may define the N (for exampleN=8) most significant bits of the system frame number. The M (forexample M=2) least significant bits of the SFN may be acquiredimplicitly in the PBCH decoding. For example, timing of a 40 ms PBCH TTImay indicate 2 least significant bits (within 40 ms PBCH TTI, the firstradio frame: 00, the second radio frame: 01, the third radio frame: 10,the last radio frame: 11). One value may apply for other carriers in thesame sector of a base station (the associated functionality is common(e.g. not performed independently for each cell). PHICH configuration(s)may include PHICH duration, which may be normal (e.g. one symbolduration) or extended (e.g. 3 symbol duration).

Physical control format indicator channel(s) (PCFICH) may carryinformation about the number of OFDM symbols used for transmission ofPDCCHs (physical downlink control channel) in a subframe. The set ofOFDM symbols possible to use for PDCCH in a subframe may depend on manyparameters including, for example, downlink carrier bandwidth, in termsof downlink resource blocks. PCFICH transmitted in one subframe may bescrambled with cell-specific sequence(s) prior to modulation, resultingin a block of scrambled bits. A scrambling sequence generator(s) may beinitialized at the start of subframe(s). Block (s) of scrambled bits maybe modulated using QPSK. Block(s) of modulation symbols may be mapped toat least one layer and precoded resulting in a block of vectorsrepresenting the signal for at least one antenna port. Instances ofPCFICH control channel(s) may indicate one of several (e.g. 3) possiblevalues after being decoded. The range of possible values of instance(s)of the first control channel may depend on the first carrier bandwidth.

According to some of the various embodiments, physical downlink controlchannel(s) may carry scheduling assignments and other controlinformation. The number of resource-elements not assigned to PCFICH orPHICH may be assigned to PDCCH. PDCCH may support multiple formats.Multiple PDCCH packets may be transmitted in a subframe. PDCCH may becoded by tail biting convolutionally encoder before transmission. PDCCHbits may be scrambled with a cell-specific sequence prior to modulation,resulting in block(s) of scrambled bits. Scrambling sequencegenerator(s) may be initialized at the start of subframe(s). Block(s) ofscrambled bits may be modulated using QPSK. Block(s) of modulationsymbols may be mapped to at least one layer and precoded resulting in ablock of vectors representing the signal for at least one antenna port.PDCCH may be transmitted on the same set of antenna ports as the PBCH,wherein PBCH is a physical broadcast channel broadcasting at least onebasic system information field.

According to some of the various embodiments, scheduling controlpacket(s) may be transmitted for packet(s) or group(s) of packetstransmitted in downlink shared channel(s). Scheduling control packet(s)may include information about subcarriers used for packettransmission(s). PDCCH may also provide power control commands foruplink channels. OFDM subcarriers that are allocated for transmission ofPDCCH may occupy the bandwidth of downlink carrier(s). PDCCH channel(s)may carry a plurality of downlink control packets in subframe(s). PDCCHmay be transmitted on downlink carrier(s) starting from the first OFDMsymbol of subframe(s), and may occupy up to multiple symbol duration(s)(e.g. 3 or 4).

According to some of the various embodiments, PHICH may carry thehybrid-ARQ (automatic repeat request) ACK/NACK. Multiple PHICHs mappedto the same set of resource elements may constitute a PHICH group, wherePHICHs within the same PHICH group may be separated through differentorthogonal sequences. PHICH resource(s) may be identified by the indexpair (group, sequence), where group(s) may be the PHICH group number(s)and sequence(s) may be the orthogonal sequence index within thegroup(s). For frame structure type 1, the number of PHICH groups maydepend on parameters from higher layers (RRC). For frame structure type2, the number of PHICH groups may vary between downlink subframesaccording to a pre-defined arrangement. Block(s) of bits transmitted onone PHICH in one subframe may be modulated using BPSK or QPSK, resultingin a block(s) of complex-valued modulation symbols. Block(s) ofmodulation symbols may be symbol-wise multiplied with an orthogonalsequence and scrambled, resulting in a sequence of modulation symbols

Other arrangements for PCFICH, PHICH, PDCCH, and/or PDSCH may besupported. The configurations presented here are for example purposes.In another example, resources PCFICH, PHICH, and/or PDCCH radioresources may be transmitted in radio resources including a subset ofsubcarriers and pre-defined time duration in each or some of thesubframes. In an example, PUSCH resource(s) may start from the firstsymbol. In another example embodiment, radio resource configuration(s)for PUSCH, PUCCH, and/or PRACH (physical random access channel) may usea different configuration. For example, channels may be timemultiplexed, or time/frequency multiplexed when mapped to uplink radioresources.

According to some of the various aspects of embodiments, a wirelessdevice may be preconfigured with one or more carriers. When the wirelessdevice is configured with more than one carrier, the base station and/orwireless device may activate and/or deactivate the configured carriers.One of the carriers (the primary carrier) may always be activated. Othercarriers may be deactivated by default and/or may be activated by a basestation when needed. A base station may activate and deactivate carriersby sending an activation/deactivation MAC control element. Furthermore,the UE may maintain a carrier deactivation timer per configured carrierand deactivate the associated carrier upon its expiry. The same initialtimer value may apply to instance(s) of the carrier deactivation timer.The initial value of the timer may be configured by a network. Theconfigured carriers (unless the primary carrier) may be initiallydeactivated upon addition and after a handover.

According to some of the various aspects of embodiments, if a wirelessdevice receives an activation/deactivation MAC control elementactivating the carrier, the wireless device may activate the carrier,and/or may apply normal carrier operation including: sounding referencesignal transmissions on the carrier, CQI (channel qualityindicator)/PMI(precoding matrix indicator)/RI(ranking indicator)reporting for the carrier, PDCCH monitoring on the carrier, PDCCHmonitoring for the carrier, start or restart the carrier deactivationtimer associated with the carrier, and/or the like. If the devicereceives an activation/deactivation MAC control element deactivating thecarrier, and/or if the carrier deactivation timer associated with theactivated carrier expires, the base station or device may deactivate thecarrier, and may stop the carrier deactivation timer associated with thecarrier, and/or may flush HARQ buffers associated with the carrier.

In this specification, “a” and “an” and similar phrases are to beinterpreted as “at least one” and “one or more.” In this specification,the term “may” is to be interpreted as “may, for example,” In otherwords, the term “may” is indicative that the phrase following the term“may” is an example of one of a multitude of suitable possibilities thatmay, or may not, be employed to one or more of the various embodiments.If A and B are sets and every element of A is also an element of B, A iscalled a subset of B. In this specification, only non-empty sets andsubsets are considered. For example, possible subsets of B={cell1,cell2} are: {cell1}, {cell2}, and {cell1, cell2}.

Many of the elements described in the disclosed embodiments may beimplemented as modules. A module is defined here as an isolatableelement that performs a defined function and has a defined interface toother elements. The modules described in this disclosure may beimplemented in hardware, software in combination with hardware,firmware, wetware (i.e hardware with a biological element) or acombination thereof, all of which are behaviorally equivalent. Forexample, modules may be implemented as a software routine written in acomputer language configured to be executed by a hardware machine (suchas C, C++, Fortran, Java, Basic, Matlab or the like) or amodeling/simulation program such as Simulink, Stateflow, GNU Octave, orLab VIEWMathScript. Additionally, it may be possible to implementmodules using physical hardware that incorporates discrete orprogrammable analog, digital and/or quantum hardware. Examples ofprogrammable hardware comprise: computers, microcontrollers,microprocessors, application-specific integrated circuits (ASICs); fieldprogrammable gate arrays (FPGAs); and complex programmable logic devices(CPLDs). Computers, microcontrollers and microprocessors are programmedusing languages such as assembly, C, C++ or the like. FPGAs, ASICs andCPLDs are often programmed using hardware description languages (HDL)such as VHSIC hardware description language (VHDL) or Verilog thatconfigure connections between internal hardware modules with lesserfunctionality on a programmable device. Finally, it needs to beemphasized that the above mentioned technologies are often used incombination to achieve the result of a functional module.

The disclosure of this patent document incorporates material which issubject to copyright protection. The copyright owner has no objection tothe facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the Patent and Trademark Officepatent file or records, for the limited purposes required by law, butotherwise reserves all copyright rights whatsoever.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevantart(s) that various changes in form and detail can be made thereinwithout departing from the spirit and scope. In fact, after reading theabove description, it will be apparent to one skilled in the relevantart(s) how to implement alternative embodiments. Thus, the presentembodiments should not be limited by any of the above describedexemplary embodiments. In particular, it should be noted that, forexample purposes, the above explanation has focused on the example(s)using FDD communication systems. However, one skilled in the art willrecognize that embodiments of the invention may also be implemented inTDD communication systems. The disclosed methods and systems may beimplemented in wireless or wireline systems. The features of variousembodiments presented in this invention may be combined. One or manyfeatures (method or system) of one embodiment may be implemented inother embodiments. Only a limited number of example combinations areshown to indicate to one skilled in the art the possibility of featuresthat may be combined in various embodiments to create enhancedtransmission and reception systems and methods.

In addition, it should be understood that any figures which highlightthe functionality and advantages, are presented for example purposesonly. The disclosed architecture is sufficiently flexible andconfigurable, such that it may be utilized in ways other than thatshown. For example, the actions listed in any flowchart may bere-ordered or only optionally used in some embodiments.

Further, the purpose of the Abstract of the Disclosure is to enable theU.S. Patent and Trademark Office and the public generally, andespecially the scientists, engineers and practitioners in the art whoare not familiar with patent or legal terms or phraseology, to determinequickly from a cursory inspection the nature and essence of thetechnical disclosure of the application. The Abstract of the Disclosureis not intended to be limiting as to the scope in any way.

Finally, it is the applicant's intent that only claims that include theexpress language “means for” or “step for” be interpreted under 35U.S.C. 112, paragraph 6. Claims that do not expressly include the phrase“means for” or “step for” are not to be interpreted under 35 U.S.C. 112,paragraph 6.

What is claimed is:
 1. A method comprising: a) receiving, by a servingbase station, a first message from a wireless device on a carrier, saidfirst message comprising one or more parameters implicitly or explicitlyindicating whether said wireless device supports configuration of: i) amaximum of k channel state information reference signals for saidcarrier, k being an integer greater than one; and ii) a maximum of nchannel state information interference measurement resources for saidcarrier, n being an integer greater than one; b) transmitting, by saidserving base station to said wireless device, at least one secondmessage, at least some parameters in said at least one second messagedepend at least in part on said first message, said at least one secondmessage: i) comprising: (1) one or more channel state informationreference signals parameters; (2) one or more channel state informationinterference measurement resources parameters; and (3) a plurality ofmeasurement parameters; ii) configured to cause: (1) configuration of jchannel state information reference signals for said carrier, j being aninteger smaller than or equal to k; and (2) configuration of m channelstate information interference measurement resources for said carrier, mbeing an integer smaller than or equal to n; and (3) said wirelessdevice measuring signal quality of at least one carrier of one or moretarget base stations in response to said measurement parameters; c)receiving, by said serving base station, at least one measurement reportfrom said wireless device in response to said at least one secondmessage, said at least one measurement report comprising signal qualityinformation of at least one carrier said at least one carrier of atleast one of said one or more target base stations, said signal qualityinformation derived at least in part employing measurements of at leastone OFDM subcarrier; d) making a handover decision, by said serving basestation, based at least in part on said at least one measurement report;e) transmitting, by said serving base station, in response to saidserving base station making a handover decision for said wirelessdevice, at least one third message to at least one target base station,said at least one third message comprising: i) said one or moreparameters implicitly or explicitly indicating whether said wirelessdevice supports said configuration of: (1) said maximum of k channelstate information reference signals; and (2) said maximum of n channelstate information interference measurement resources; ii) configurationparameters of: (1) said j channel state information reference signalsfor said carrier; and (2) said m channel state information interferencemeasurement resources for said carrier.
 2. The method of claim 1, beforesaid at least one second message is transmitted, further comprising: a)encrypting said at least one second message; and a) protecting said atleast one second message by an integrity header.
 3. The method of claim1, wherein said at least one second message: a) further includesconfiguration information for physical channels for said wirelessdevice; and b) is configured to cause said wireless device to set up ormodify at least one radio bearer.
 4. The method of claim 1, wherein oneof said at least one second message is configured to cause said wirelessdevice to configure at least one of a physical layer parameter, a mediaaccess control layer parameter and a radio link control layer parameter.5. The method of claim 1, wherein one of said at least one secondmessage comprises radio link configuration information comprising uplinkchannel configuration parameters and handover parameters.
 6. The methodof claim 1, wherein one of said at least one second message comprisesradio resource configuration parameters comprising a physical channelconfiguration parameters.
 7. The method of claim 1, further comprisingsaid serving base station transmitting a demodulation reference signalon said carrier.
 8. A method comprising: a) receiving, by a serving basestation, a first message from a wireless device on a carrier, said firstmessage comprising one or more parameters implicitly or explicitlyindicating whether said wireless device supports configuration of: i) amaximum of k channel state information reference signals for saidcarrier, k being an integer greater than one; and ii) a maximum of nchannel state information interference measurement resources for saidcarrier, n being an integer greater than one; b) transmitting, by saidserving base station to said wireless device, at least one secondmessage, at least some parameters in said at least one second messagedepend at least in part on said first message, said at least one secondmessage configured to cause configuration of: i) j channel stateinformation reference signals for said carrier, j being an integersmaller than or equal to k; and ii) m channel state informationinterference measurement resources for said carrier, m being an integersmaller than or equal to n; and c) transmitting, by said serving basestation, in response to said serving base station making a handoverdecision for said wireless device, at least one third message to atleast one target base station, said at least one third messagecomprising at least one of: i) said one or more parameters implicitly orexplicitly indicating whether said wireless device supports saidconfiguration of: (1) said maximum of k channel state informationreference signals; and (2) said maximum of n channel state informationinterference measurement resources; ii) configuration parameters of: (1)said j channel state information reference signals for said carrier; and(2) said m channel state information interference measurement resourcesfor said carrier.
 9. The method of claim 8, wherein said at least onesecond message comprises said configuration parameters of: a) said jchannel state information reference signals for said carrier; and a)said m channel state information interference measurement resources forsaid carrier.
 10. The method of claim 8, wherein said at least onesecond message: a) comprises a plurality of measurement parameters; andb) is configured to cause said wireless device measuring signal qualityof at least one carrier of one or more target base stations in responseto said measurement parameters.
 11. The method of claim 10, furthercomprising: a) receiving, by said serving base station, at least onemeasurement report from said wireless device in response to said atleast one second message, said at least one measurement reportcomprising signal quality information of at least one carrier of said atleast one carrier of at least one of said one or more target basestations, said signal quality information derived at least in partemploying measurements of at least one OFDM subcarrier; b) making ahandover decision, by said serving base station, based at least in parton said at least one measurement report.
 12. The method of claim 11,wherein a format of said at least one measurement report is determinedemploying at least one of said at least one second control message. 13.The method of claim 8, wherein said at least one second message: a)comprises an identifier for each carrier in a plurality of carriers; andb) configured to cause configuration of: i) said plurality of carriersin said wireless device; ii) one or more channel state informationreference signals for one or more carriers in said plurality ofcarriers; and iii) one or more channel state information interferencemeasurement resources for one or more carriers in said plurality ofcarriers.
 14. The method of claim 8, wherein one of said at least onesecond message comprises radio link configuration information comprisinguplink channel configuration parameters and handover parameters.
 15. Themethod of claim 8, wherein one of said at least one second messagecomprises at least one radio resource configuration parameter comprisingat least one physical channel configuration parameter.
 16. A servingbase station, configured to communicate employing at least one backwardcompatible carrier and at least one non-backward compatible carrier,comprising: a) one or more communication interfaces; b) one or moreprocessors; and c) memory storing instructions that, when executed,cause said serving base station to: i) receive a first message from awireless device on a carrier, said first message comprising one or moreparameters implicitly or explicitly indicating whether said wirelessdevice supports configuration of: (1) a maximum of k channel stateinformation reference signals for said carrier, k being an integergreater than one; and (2) a maximum of n channel state informationinterference measurement resources for said carrier, n being an integergreater than one; ii) transmit to said wireless device, at least onesecond message, at least some parameters in said at least one secondmessage depend at least in part on said first message, said at least onesecond message configured to cause configuration of: (1) j channel stateinformation reference signals for said carrier, j being an integersmaller than or equal to k; and (2) m channel state informationinterference measurement resources for said carrier, m being an integersmaller than or equal to n; and iii) transmit in response to saidserving base station making a handover decision for said wirelessdevice, at least one third message to at least one target base station,said at least one third message comprising at least one of: (1) said oneor more parameters implicitly or explicitly indicating whether saidwireless device supports said configuration of: (a) said maximum of kchannel state information reference signals; and (b) said maximum of nchannel state information interference measurement resources; (2)configuration parameters of: (a) said j channel state informationreference signals for said carrier; and (b) said m channel stateinformation interference measurement resources for said carrier.
 17. Theserving base station of claim 16, wherein said instructions, whenexecuted, further causes said serving base station, before said at leastone second message is transmitted, to: a) encrypt said at least onesecond message; and b) protect said at least one second message by anintegrity header.
 18. The serving base station of claim 16, wherein saidat least one second message: a) further includes configurationinformation for physical channels for said wireless device; and b)configured to cause said wireless device to set up or modify at leastone radio bearer.
 19. The serving base station of claim 16, wherein oneof said at least one second message configured to cause said wirelessdevice to configure at least one of a physical layer parameter, a mediaaccess control layer parameter and a radio link control layer parameter.20. The serving base station of claim 16, wherein one of said at leastone second message comprises radio link configuration informationcomprising uplink channel configuration parameters and handoverparameters.